fwts: maxreadreq should explain why a low setting is bad

The fwts maxreadreq test gives rather too little information regarding why a low MaxReadReq PCI setting is bad. It should contain a message such as:

"The MaxReadRequest size is set too low and will affect performance. It will provide excellent bus sharing at the cost of bus data transfer rates. Although not a critical issue, it may be worth considering setting the MaxReadRequest size to 256 or 512 to increase throughput on the PCI Express bus. Some drivers (for example the Brocade Fibre Channel driver) allow one to override the firmware settings. Perhaps this is a BIOS configuration setting that can be modified, if so, it may be worth increasing it."