af_packet: remove unnecessary BUG_ON() in tpacket_destruct_skb

If skb is NULL, then stack trace is thrown anyway on dereference.
Therefore, the stack trace triggered by BUG_ON is duplicate.
Signed-off-by: NDaniel Borkmann <danborkmann@googlemail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -1968,8 +1968,6 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
 	struct packet_sock *po = pkt_sk(skb->sk);
 	void *ph;
 
-	BUG_ON(skb == NULL);
-
 	if (likely(po->tx_ring.pg_vec)) {
 		ph = skb_shinfo(skb)->destructor_arg;
 		BUG_ON(__packet_get_status(po, ph) != TP_STATUS_SENDING);