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/drivers/net/wireless/ath/carl9170/fw.c b/drivers/net/wireless/ath/carl9170/fw.c
index cffde8d..5c73c03 100644
--- a/drivers/net/wireless/ath/carl9170/fw.c
+++ b/drivers/net/wireless/ath/carl9170/fw.c
@@ -355,6 +355,8 @@
 
 	ar->hw->wiphy->interface_modes |= if_comb_types;
 
+	ar->hw->wiphy->flags |= WIPHY_FLAG_HAS_REMAIN_ON_CHANNEL;
+
 #undef SUPPORTED
 	return carl9170_fw_tx_sequence(ar);
 }