mac80211: remove fragmentation offload functionality

There's no driver that actually does fragmentation on the
device, and the callback is buggy (when it returns an error,
mac80211's fragmentation status is changed so reading the
frag threshold from userspace reads the new value despite
the error). Let's just remove it, if we really find some
hardware supporting it we can add it back later.

Signed-off-by: Johannes Berg <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

include/net/mac80211.h

···
  *
  * @set_rts_threshold: Configuration of RTS threshold (if device needs it)
  *
- * @set_frag_threshold: Configuration of fragmentation threshold. Assign this if
- *	the device does fragmentation by itself; if this method is assigned then
- *	the stack will not do fragmentation.
- *
  * @sta_notify: Notifies low level driver about addition or removal of an
  *	associated station, AP, IBSS/WDS/mesh peer etc. Must be atomic.
  *
···
 	void (*get_tkip_seq)(struct ieee80211_hw *hw, u8 hw_key_idx,
 			     u32 *iv32, u16 *iv16);
 	int (*set_rts_threshold)(struct ieee80211_hw *hw, u32 value);
-	int (*set_frag_threshold)(struct ieee80211_hw *hw, u32 value);
 	void (*sta_notify)(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 			enum sta_notify_cmd, struct ieee80211_sta *sta);
 	void (*sta_notify_ps)(struct ieee80211_hw *hw,

net/mac80211/tx.c

···
 	if (tx->flags & IEEE80211_TX_FRAGMENTED) {
 		if ((tx->flags & IEEE80211_TX_UNICAST) &&
 		    skb->len + FCS_LEN > local->fragmentation_threshold &&
-		    !local->ops->set_frag_threshold &&
 		    !(info->flags & IEEE80211_TX_CTL_AMPDU))
 			tx->flags |= IEEE80211_TX_FRAGMENTED;
 		else

net/mac80211/wext.c

···
 		local->fragmentation_threshold = frag->value & ~0x1;
 	}
 
-	/* If the wlan card performs fragmentation in hardware/firmware,
-	 * configure it here */
-
-	if (local->ops->set_frag_threshold)
-		return local->ops->set_frag_threshold(
-			local_to_hw(local),
-			local->fragmentation_threshold);
-
 	return 0;
 }