messages/MOSDMap: significant feature bits.

messages/MOSDMap: significant feature bits.

1. MOSDMap go with features indicating the features
this map encoded for.

2. Only reencode if significant bits mismatch between
target features and my features.

also update mon/OSDMonitor and osd/OSDService to adopt this change.

Signed-off-by: Xiaoxi CHEN <xiaoxchen@ebay.com>
(cherry picked from commit dc7a219468b5a9313b5a1d660c1b61e1e35b718d)

Conflicts:
	src/messages/MOSDMap.h
            drop COMPACT_VERSION
	src/mon/OSDMonitor.cc
            drop get_removed_snaps_range
   Both introduced by post-luminous commit 49833c3bb264949b8126796997a95a95b50af411