MFC: r221014,r221018

MFC: r221014,r221018
Modify the experimental NFS client so that it uses the same
"struct nfs_args" as the regular NFS client. This is needed
so that the old mount(2) syscall will work and it makes
sharing of the diskless NFS root code easier. Eary in the
porting exercise I introduced a new revision of nfs_args, but
didn't actually need it, thanks to nmount(2). I re-introduced the
NFSMNT_KERB flag, since it does essentially the same thing and
the old one would not have been used because it never worked.
I also added a few new NFSMNT_xxx flags to sys/nfsclient/nfs_args.h
that are used by the experimental NFS client.
Also fix the NFS client so that it doesn't bogusly set the
f_flags argument of "struct statfs",

git-svn-id: svn://svn.freebsd.org/base/stable/8@221871 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f