mac80211: remove warning from ieee80211_beacon_loss

Currently, mac80211 assumes that connection monitor offload
for BSS station implies that the device:
- sends periodic keep alive packets to associated AP
- monitors missed beacons
- actively probes the AP in case of missed beacons

In case of poor connection conditions it expects the function
ieee80211_connection_loss() to be called by driver. However,
some devices implement connection monitor offload excluding
active AP probing.

To allow them to call ieee80211_beacon_loss() cleanly, remove
the warning there and thus allow them to use mac80211 for the
AP probing even if connection monitor offload is supported.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>