mac80211: remove BUG_ON usage

These BUG_ON statements should never trigger, but in the unlikely
event that somebody does manage don't stop everything but simply
exit the code path with an error.

Leave the one BUG_ON where changing it would result in a NULL
pointer dereference.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/mesh_sync.c b/net/mac80211/mesh_sync.c
index 2bc5dc2..09625d6 100644
--- a/net/mac80211/mesh_sync.c
+++ b/net/mac80211/mesh_sync.c
@@ -171,7 +171,7 @@
 	u8 cap;
 
 	WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
-	BUG_ON(!rcu_read_lock_held());
+	WARN_ON(!rcu_read_lock_held());
 	cap = beacon->meshconf->meshconf_cap;
 
 	spin_lock_bh(&ifmsh->sync_offset_lock);