xen: ease cloning of virtual images by disabling mac address rules

Similarly to LP #341006 other hypervisor MAC address prefixes should be added to the ignore list.

Currently (Oneiric), /lib/udev/rules.d/75-persistent-net-generator.rules has:

# ignore KVM virtual interfaces
ENV{MATCHADDR}=="52:54:00:*", GOTO="persistent_net_generator_end"
# ignore VMWare virtual interfaces
ENV{MATCHADDR}=="00:0c:29:*|00:50:56:*", GOTO="persistent_net_generator_end"
# ignore Hyper-V virtual interfaces
ENV{MATCHADDR}=="00:15:5d:*", GOTO="persistent_net_generator_end"
# ignore Eucalyptus virtual interfaces
ENV{MATCHADDR}=="d0:0d:*", GOTO="persistent_net_generator_end"

this list should be expanded to include:

00:16:3e:* (xen, default range used in xen3)

(see, e.g.
  http://www.coffer.com/mac_find/?string=00%3A16%3A3E
)

These are not caught by:

# ignore Xen virtual interfaces
SUBSYSTEMS=="xen", GOTO="persistent_net_generator_end"

when on HVM mode without PV drivers, as the device appears as "eth0".

Ideally this would be fixed from Lucid onwards, but should certainly be fixed for Precise.