mac80211: introduce TDLS channel switch ops

Implement the cfg80211 TDLS channel switch ops and introduce new mac80211
ones for low-level drivers.
Verify low-level driver support for the new ops when using the relevant
wiphy feature bit. Also verify the peer supports channel switching before
passing the command down.

Add a new STA flag to track the off-channel state with the TDLS peer and
make sure to cancel the channel-switch if the peer STA is unexpectedly
removed.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 282a4f3..774ccb2 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -764,6 +764,11 @@
 	     local->hw.offchannel_tx_hw_queue >= local->hw.queues))
 		return -EINVAL;
 
+	if ((hw->wiphy->features & NL80211_FEATURE_TDLS_CHANNEL_SWITCH) &&
+	    (!local->ops->tdls_channel_switch ||
+	     !local->ops->tdls_cancel_channel_switch))
+		return -EOPNOTSUPP;
+
 #ifdef CONFIG_PM
 	if (hw->wiphy->wowlan && (!local->ops->suspend || !local->ops->resume))
 		return -EINVAL;