cxgb4: Use kfree_skb for skb pointers

Use kfree_skb for skb pointers

Acked-by: Dimitris Michailidis <dm@chelsio.com>
Signed-off-by: Denis Kirjanov <dkirjanov@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>