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>