e NFS v4 xdev mount function

I can now share this code with the v2 and v3 code by using the NFS
subversion structure.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
(|œ¢‘+x