ipv6: cleanup: remove unneeded null check

We dereference "sk" unconditionally elsewhere in the function.  

This was left over from:  b30bd282 "ip6_xmit: remove unnecessary NULL
ptr check".  According to that commit message, "the sk argument to 
ip6_xmit is never NULL nowadays since the skb->priority assigment 
expects a valid socket."
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -218,8 +218,7 @@ int ip6_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl,
 			}
 			kfree_skb(skb);
 			skb = skb2;
-			if (sk)
-				skb_set_owner_w(skb, sk);
+			skb_set_owner_w(skb, sk);
 		}
 		if (opt->opt_flen)
 			ipv6_push_frag_opts(skb, opt, &proto);