xfrm4: Invalidate all ipv4 routes on IPsec pmtu events

On IPsec pmtu events we can't access the transport headers of
the original packet, so we can't find the socket that sent
the packet. The only chance to notify the socket about the
pmtu change is to force a relookup for all routes. This
patch implenents this for the IPsec protocols.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index fd26ff4..3b4f0cd 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -502,9 +502,12 @@
 	if (!x)
 		return;
 
-	if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH)
+	if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH) {
+		atomic_inc(&flow_cache_genid);
+		rt_genid_bump(net);
+
 		ipv4_update_pmtu(skb, net, info, 0, 0, IPPROTO_ESP, 0);
-	else
+	} else
 		ipv4_redirect(skb, net, 0, 0, IPPROTO_ESP, 0);
 	xfrm_state_put(x);
 }