nfsd: allow DELEGRETURN on directories

nfsd: allow DELEGRETURN on directories

As Trond pointed out: "...provided that the presented stateid is
actually valid, it is also sufficient to uniquely identify the file to
which it is associated (see RFC8881 Section 8.2.4), so the filehandle
should be considered mostly irrelevant for operations like DELEGRETURN."

Don't ask fh_verify to filter on file type.

Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20251111-dir-deleg-ro-v6-15-52f3feebb2f2@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>