NFS: Call nfs_probe_server() during a fscontext-reconfigure event

This lets us update the server's attributes when the user does a "mount
-o remount" on the filesystem.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>