mon/OSDMonitor: set last_force_op_resend on overlay pool too

mon/OSDMonitor: set last_force_op_resend on overlay pool too

We currently set the last_force_op_resend field on the
base pool when we set or clear the overlay.  Set it on
the cache/overlay pool too.  The Objecter should resend
even with a change only to the base pool, but the OSD
needs to see the change on the overlay pool to correctly
discard the op.

Fixes: http://tracker.ceph.com/issues/18366
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 08c3618771b852840aa88cff1ca98d980d802941)