NFS4: Set parsed mount data version to 4

This patch only affects mounting through "-t nfs4" since it doesn't set
up an nfs version to use in the mount data.  The nfs client was trying
to mount using NFS v0, causing either a BUG() or a protocol not
supported message.

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