Build failure on CentOS 6

Yura reported that library fails to build on CentOS 6 because the autogen.sh script generates invalid shell code for configure script (related to libpcap).

# gcc --version
gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# ./autogen.sh --disable-rohc-apps --disable-rohc-stats
--disable-rohc-tests --disable-doc
Running aclocal... done
Running libtoolize... done
Running autoconf... done
Running autoheader... done
Running automake... done
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking how to create a pax tar archive... gnutar
checking build system type... i686-pc-linux-gnu
checking host system type... i686-pc-linux-gnu
checking for style of include used by make... GNU
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking dependency style of gcc... gcc3
checking for a sed that does not truncate output... /bin/sed
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for fgrep... /bin/grep -F
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for BSD- or MS-compatible name lister (nm)... /usr/bin/nm -B
checking the name lister (/usr/bin/nm -B) interface... BSD nm
checking whether ln -s works... yes
checking the maximum length of command line arguments... 1966080
checking whether the shell understands some XSI constructs... yes
checking whether the shell understands "+="... yes
checking for /usr/bin/ld option to reload object files... -r
checking for objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for ar... ar
checking for strip... strip
checking for ranlib... ranlib
checking command to parse /usr/bin/nm -B output from gcc object... ok
checking how to run the C preprocessor... gcc -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for dlfcn.h... yes
checking for objdir... .libs
checking if gcc supports -fno-rtti -fno-exceptions... no
checking for gcc option to produce PIC... -fPIC -DPIC
checking if gcc PIC flag -fPIC -DPIC works... yes
checking if gcc static flag -static works... no
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.o... (cached) yes
checking whether the gcc linker (/usr/bin/ld) supports shared
libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... no
checking for gcc... (cached) gcc
checking whether we are using the GNU C compiler... (cached) yes
checking whether gcc accepts -g... (cached) yes
checking for gcc option to accept ISO C89... (cached) none needed
checking dependency style of gcc... (cached) gcc3
checking for a BSD-compatible install... /usr/bin/install -c
checking stdio.h usability... yes
checking stdio.h presence... yes
checking for stdio.h... yes
checking for stdlib.h... (cached) yes
checking for string.h... (cached) yes
checking for strings.h... (cached) yes
checking time.h usability... yes
checking time.h presence... yes
checking for time.h... yes
checking sys/time.h usability... yes
checking sys/time.h presence... yes
checking for sys/time.h... yes
checking arpa/inet.h usability... yes
checking arpa/inet.h presence... yes
checking for arpa/inet.h... yes
checking winsock2.h usability... no
checking winsock2.h presence... no
checking for winsock2.h... no
checking linux/if_tun.h usability... yes
checking linux/if_tun.h presence... yes
checking for linux/if_tun.h... yes
checking sched.h usability... yes
checking sched.h presence... yes
checking for sched.h... yes
checking sys/mman.h usability... yes
checking sys/mman.h presence... yes
checking for sys/mman.h... yes
checking for inline... inline
checking whether byte ordering is bigendian... no
checking for gcc option to accept ISO C99... -std=gnu99
checking for malloc... yes
checking for calloc... yes
checking for free... yes
checking for memcpy... yes
checking for memcmp... yes
checking for ntohl... yes
checking for htonl... yes
checking for ntohs... yes
checking for htons... yes
checking for sched_setscheduler... yes
checking how many arguments sched_setscheduler takes... 3
checking for uint8_t... yes
checking for uint16_t... yes
checking for uint32_t... yes
checking host system type... (cached) i686-pc-linux-gnu
./configure: line 15677: syntax error near unexpected token `else'
./configure: line 15677: `else'