mac80211: don't always advertise remain-on-channel

Not all devices are really capable of implementing
remain-on-channel, even if it is implemented in SW,
as they can't necessarily deal with channel changes
while associated.

Remove the WIPHY_FLAG_HAS_REMAIN_ON_CHANNEL and add
it only if either the driver has remain_on_channel
implemented in the driver/device.

Also add it to all drivers that advertise P2P right
now since those definitely have to have it working.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 1633648..d019f0d 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -557,8 +557,10 @@
 			WIPHY_FLAG_4ADDR_AP |
 			WIPHY_FLAG_4ADDR_STATION |
 			WIPHY_FLAG_REPORTS_OBSS |
-			WIPHY_FLAG_OFFCHAN_TX |
-			WIPHY_FLAG_HAS_REMAIN_ON_CHANNEL;
+			WIPHY_FLAG_OFFCHAN_TX;
+
+	if (ops->remain_on_channel)
+		wiphy->flags |= WIPHY_FLAG_HAS_REMAIN_ON_CHANNEL;
 
 	wiphy->features = NL80211_FEATURE_SK_TX_STATUS |
 			  NL80211_FEATURE_HT_IBSS;