cfg80211: remove remain-on-channel channel type

As mwifiex (and mac80211 in the software case) are the
only drivers actually implementing remain-on-channel
with channel type, userspace can't be relying on it.
This is the case, as it's used only for P2P operations
right now.

Rather than adding a flag to tell userspace whether or
not it can actually rely on it, simplify all the code
by removing the ability to use different channel types.
Leave only the validation of the attribute, so that if
we extend it again later (with the needed capability
flag), it can't break userspace sending invalid data.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -2550,7 +2550,6 @@ struct ieee80211_ops {
 	int (*remain_on_channel)(struct ieee80211_hw *hw,
 				 struct ieee80211_vif *vif,
 				 struct ieee80211_channel *chan,
-				 enum nl80211_channel_type channel_type,
 				 int duration);
 	int (*cancel_remain_on_channel)(struct ieee80211_hw *hw);
 	int (*set_ringparam)(struct ieee80211_hw *hw, u32 tx, u32 rx);