messages/MOSDMap: do compat reencode of crush map, too

messages/MOSDMap: do compat reencode of crush map, too

If we are reencoding an incremental, and it embeds a crush map, we need
to reencode that in a compatible way too.  This is especially true now
because we have the compat crush weight-sets.  Otherwise, a client may
learn the crush map through an incremental but not understand choose_args,
and not see/understand the alternate weight set.  It will send requests
to the wrong OSDs where they will just get dropped.

Fixes: http://tracker.ceph.com/issues/21882
Signed-off-by: Sage Weil <sage@redhat.com>