osd: make the PG's SORTBITWISE assert a more generous shutdown

osd: make the PG's SORTBITWISE assert a more generous shutdown

We want to stop working if we get activated while sortbitwise is not set
on the cluster, but we might have old maps where it wasn't if the flag
was changed recently. And doing it in the PG code was a bit silly anyway.

Instead check SORTBITWISE in the main OSDMap handling code prior to
prepublishing it. Let it go through if we aren't active at the time.

Fixes: http://tracker.ceph.com/issues/20416
Signed-off-by: Greg Farnum <gfarnum@redhat.com>