NFS: Fix a default mount regression...

With the recent spate of changes, the nfs protocol version will now default
to 2 instead of 3, while the mount protocol version defaults to 3.

The following patch should ensure the defaults are consistent with the
previous defaults of vers=3,proto=tcp,mountvers=3,mountproto=tcp.

This fixes the bug
   http://bugzilla.kernel.org/show_bug.cgi?id=14259

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>