s3:vfs:gpfs: fix logic when gpfs:winattr is false (the default!)

s3:vfs:gpfs: fix logic when gpfs:winattr is false (the default!)

On my autocluster setup, it's not set.  Maybe it should be?  Otherwise
smbclient and some Windows client programs will get errors like:

        # smbclient //localhost/data -Uadministrator%XXX
        Domain=[VSOFS1] OS=[Unix] Server=[Samba 3.4.2-ctdb-10]
        smb: \> put /etc/resolv.conf resolv.conf
        NT_STATUS_ACCESS_DENIED closing remote file \resolv.conf
        smb: \>

Caused by attempting to update the time on close.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Michael Adam <obnox@samba.org>
(cherry picked from commit 385d925f7e0fedca7d480e4f25d89e3194433b88)

Fix bug #7498 (robocopy fails to a GPFS share when setting the date).