mon: do not send duplicated osdmap msg to not sync'ed osd

mon: do not send duplicated osdmap msg to not sync'ed osd

prior to this change:
a peon may forward the pgstats to leader, and record it locally, but leader will
check if osd has the latest map before process, if not, will use a route op to
indicate peon to send it, then poen will delete routed op when fininaly send
out which make peon cannot send pgstatack when leader has processed the
pgstat update. so osd will always track it util reach a threshold block pgstats
sending, at worst, reopen mon session.
also, both leader and peon will send out the osdmap message to the osd.

after this change:
only the peon will send out the osdmap message. and the pgstatack message
will be routed to the osd as expected. so the osd will not keep track of the
"acked" pg stats in its queue forever before times out.

Fixes: http://tracker.ceph.com/issues/18458
Signed-off-by: Mingxin Liu <mingxin@xsky.com>