mac80211: rewrite fragmentation

Fragmentation currently uses an allocated array to store the
fragment skbs, and then keeps track of which have been sent
and which are still pending etc. This is rather complicated;
make it simpler by just chaining the fragments into skb->next
and removing from that list when sent. Also simplifies all
code that needs to touch fragments, since it now only needs
to walk the skb->next list.

This is a prerequisite for fixing the stored packet code,
which I need to do for proper aggregation packet storing.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ieee80211_i.h

@@ -149,11 +149,6 @@ struct ieee80211_tx_data {
 
 	struct ieee80211_channel *channel;
 
-	/* Extra fragments (in addition to the first fragment
-	 * in skb) */
-	struct sk_buff **extra_frag;
-	int num_extra_frag;
-
 	u16 ethertype;
 	unsigned int flags;
 };
@@ -191,8 +186,6 @@ struct ieee80211_rx_data {
 
 struct ieee80211_tx_stored_packet {
 	struct sk_buff *skb;
-	struct sk_buff **extra_frag;
-	int num_extra_frag;
 };
 
 struct beacon_data {