NFSv4.2: Don't send mode again in post-EXCLUSIVE4_1 SETATTR with umask

Now that we have umask support, we shouldn't re-send the mode in a SETATTR
following an exclusive CREATE, or we risk having the same problem fixed in
commit 5334c5bd ("NFS: Send attributes in OPEN request for
NFS4_CREATE_EXCLUSIVE4_1"), which is that files with S_ISGID will have that
bit stripped away.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Fixes: dff25ddb ("nfs: add support for the umask attribute")
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>