CFR: NFS root options fixup

[Sam Leffler]

There's a small patch at:

http://www.freebsd.org/~sam/nfsopts.patch

to unify parsing of nfs mount options supplied when booting over the
net.  It also extends the supported options so you can do things like
specify nolockd, tcp, udp, and nfsv2, nfsv3.  Some of this appears to be
superfluous given the work that rc.initdiskless does but it's there.

The one change I'm uncertain of is the bounds checking I apply to
rsize/wsize.

	Sam