It is illegal to dereference a skb after a successful ndo_start_xmit()
call. We must store skb length in a local variable instead.

Bug was introduced in 2.6.27 by commit 0abf77e5
(net_sched: Add accessor function for packet length for qdiscs)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>