cfg80211: make ethtool the driver's responsibility

Currently, cfg80211 tries to implement ethtool, but that doesn't
really scale well, with all the different operations. Make the
lower-level driver responsible for it, which currently only has
an effect on mac80211. It will similarly not scale well at that
level though, since mac80211 also has many drivers.

To cleanly implement this in mac80211, introduce a new file and
move some code to appropriate places.

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

net/mac80211/ieee80211_i.h

@@ -1847,6 +1847,8 @@ int ieee80211_tdls_oper(struct wiphy *wiphy, struct net_device *dev,
 			const u8 *peer, enum nl80211_tdls_operation oper);
 
 
+extern const struct ethtool_ops ieee80211_ethtool_ops;
+
 #ifdef CONFIG_MAC80211_NOINLINE
 #define debug_noinline noinline
 #else