ipsec: Don't update the pmtu on ICMPV6_DEST_UNREACH

Currently we update the pmtu in the IPsec protocol error handlers
if icmpv6 message type is either ICMPV6_DEST_UNREACH or
ICMPV6_PKT_TOOBIG. Updating the pmtu on ICMPV6_DEST_UNREACH
is wrong in any case, it causes strangely fragmented packets.
Only ICMPV6_PKT_TOOBIG signalizes pmtu discovery, so remove the
ICMPV6_DEST_UNREACH check in the IPsec protocol error handlers.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/ipv6/ipcomp6.c b/net/ipv6/ipcomp6.c
index 5636a91..ce507d9 100644
--- a/net/ipv6/ipcomp6.c
+++ b/net/ipv6/ipcomp6.c
@@ -64,8 +64,7 @@
 		(struct ip_comp_hdr *)(skb->data + offset);
 	struct xfrm_state *x;
 
-	if (type != ICMPV6_DEST_UNREACH &&
-	    type != ICMPV6_PKT_TOOBIG &&
+	if (type != ICMPV6_PKT_TOOBIG &&
 	    type != NDISC_REDIRECT)
 		return;