sit: do not confirm neighbor when do pmtu update

When do IPv6 tunnel PMTU update and calls __ip6_rt_update_pmtu() in the end,
we should not call dst_confirm_neigh() as there is no two-way communication.

v5: No change.
v4: No change.
v3: Do not remove dst_confirm_neigh, but add a new bool parameter in
dst_ops.update_pmtu to control whether we should do neighbor confirm.
Also split the big patch to small ones for each area.
v2: Remove dst_confirm_neigh in __ip6_rt_update_pmtu.

Reviewed-by: Guillaume Nault <[e-mail]>
Acked-by: David Ahern <[e-mail]>
Signed-off-by: Hangbin Liu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv6/sit.c

···
 		}
 
 		if (tunnel->parms.iph.daddr)
-			skb_dst_update_pmtu(skb, mtu);
+			skb_dst_update_pmtu_no_confirm(skb, mtu);
 
 		if (skb->len > mtu && !skb_is_gso(skb)) {
 			icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);