NFSv4.2: Fix detection of "Proxying of Times" server support

According to draft-ietf-nfsv4-delstid-07:
   If a server informs the client via the fattr4_open_arguments
   attribute that it supports
   OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS and it returns a valid
   delegation stateid for an OPEN operation which sets the
   OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag, then it MUST query the
   client via a CB_GETATTR for the fattr4_time_deleg_access (see
   Section 5.2) attribute and fattr4_time_deleg_modify attribute (see
   Section 5.2).

Thus, we should look that the server supports proxying of times via
OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS.

We want to be extra pedantic and continue to check that FATTR4_TIME_DELEG_ACCESS
and FATTR4_TIME_DELEG_MODIFY are set. The server needs to expose both for the
client to correctly detect "Proxying of Times" support.

Signed-off-by: Roi Azarzar <roi.azarzar@vastdata.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Fixes: dcb3c20f ("NFSv4: Add a capability for delegated attributes")
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>