ipv6: remove unnecessary dst_hold() in ip6_fragment()

In ipv6 tx path, rcu_read_lock() is taken so that dst won't get freed
during the execution of ip6_fragment(). Hence, no need to hold dst in
it.

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: tracywwnj

net/ipv6/ip6_output.c

@@ -698,8 +698,6 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		ipv6_hdr(skb)->payload_len = htons(first_len -
 						   sizeof(struct ipv6hdr));
 
-		dst_hold(&rt->dst);
-
 		for (;;) {
 			/* Prepare header of the next frame,
 			 * before previous one went down. */
@@ -742,15 +740,13 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		if (err == 0) {
 			IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
 				      IPSTATS_MIB_FRAGOKS);
-			ip6_rt_put(rt);
 			return 0;
 		}
 
 		kfree_skb_list(frag);
 
 		IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
 			      IPSTATS_MIB_FRAGFAILS);
-		ip6_rt_put(rt);
 		return err;
 
 slow_path_clean: