net: ipv6: fix dst ref loop in ila lwtunnel

This patch follows commit 92191dd ("net: ipv6: fix dst ref loops in
rpl, seg6 and ioam6 lwtunnels") and, on a second thought, the same patch
is also needed for ila (even though the config that triggered the issue
was pathological, but still, we don't want that to happen).

Fixes: 79ff2fc ("ila: Cache a route to translated address")
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Link: https://patch.msgid.link/20250304181039.35951-1-justin.iurman@uliege.be
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv6/ila/ila_lwt.c

@@ -88,7 +88,8 @@ static int ila_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 			goto drop;
 		}
 
-		if (ilwt->connected) {
+		/* cache only if we don't create a dst reference loop */
+		if (ilwt->connected && orig_dst->lwtstate != dst->lwtstate) {
 			local_bh_disable();
 			dst_cache_set_ip6(&ilwt->dst_cache, dst, &fl6.saddr);
 			local_bh_enable();