bpf: remove redundant null pointer check before consume_skb

consume_skb has taken the null pointer into account. hence it is safe
to remove the redundant null pointer check before consume_skb.
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/sockmap.c

@@ -590,7 +590,6 @@ static int free_sg(struct sock *sk, int start,
 		if (i == MAX_SKB_FRAGS)
 			i = 0;
 	}
-	if (md->skb)
 	consume_skb(md->skb);
 
 	return free;
@@ -973,7 +972,6 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 		if (!sg->length && md->sg_start == md->sg_end) {
 			list_del(&md->list);
-			if (md->skb)
 			consume_skb(md->skb);
 			kfree(md);
 		}