This allows the nfs_getrootfh() function to return the
correct file handle size to pxe.c for pxeboot. It also
results in NFSv2 no longer being used by default anywhere
in FreeBSD. If built with OLD_NFSV2 defined, the old
code that predated this patch will be built and NFSv2
will be used.
Tested by: danny at cs.huji.ac.il
MFC after: 2 weeks