mon/OSDMonitor: ignore boot message from before last up_from

It is possible we will have a dup OSDBoot message queued up in the mon
and will process it again after that osd was marked up and then down.  If
that happens, we should ignore this message, not mark the osd back in with
the same address.

Fixes: #8062
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1643 from ceph/wip-8062

mon/OSDMonitor: ignore boot message from before last up_from

Reviewed-by: Greg Farnum <greg@inktank.com>