mac80211: fix miscounting of ttl-dropped frames

mac80211: fix miscounting of ttl-dropped frames

[ Upstream commit a0dc02039a2ee54fb4ae400e0b755ed30e73e58c ]

In ieee80211_rx_h_mesh_fwding, we increment the 'dropped_frames_ttl'
counter when we decrement the ttl to zero.  For unicast frames
destined for other hosts, we stop processing the frame at that point.

For multicast frames, we do not rebroadcast it in this case, but we
do pass the frame up the stack to process it on this STA.  That
doesn't match the usual definition of "dropped," so don't count
those as such.

With this change, something like `ping6 -i0.2 ff02::1%mesh0` from a
peer in a ttl=1 network no longer increments the counter rapidly.

Signed-off-by: Bob Copeland <bobcopeland@fb.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>