NFS: Request fh_expire_type attribute in "server caps" operation

The fh_expire_type file attribute is a filesystem wide attribute that
consists of flags that indicate what characteristics file handles
on this FSID have.

Our client doesn't support volatile file handles.  It should find
out early (say, at mount time) whether the server is going to play
shenanighans with file handles during a migration.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>