ipv6: remove redundant null pointer check before kfree_skb

kfree_skb has taken the null pointer into account. hence it is safe
to remove the redundant null pointer check before kfree_skb.
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/af_inet6.c

@@ -468,11 +468,9 @@ void inet6_destroy_sock(struct sock *sk)
 	/* Release rx options */
 
 	skb = xchg(&np->pktoptions, NULL);
-	if (skb)
 	kfree_skb(skb);
 
 	skb = xchg(&np->rxpmtu, NULL);
-	if (skb)
 	kfree_skb(skb);
 
 	/* Free flowlabels */