rxrpc: Fix missing IPV6 #ifdef

Fix rxrpc_encap_err_rcv() to make the call to ipv6_icmp_error conditional
on IPV6 support being enabled.

Fixes: b6c66c4 ("rxrpc: Use the core ICMP/ICMP6 parsers")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org

net/rxrpc/local_object.c

@@ -33,7 +33,8 @@ static void rxrpc_encap_err_rcv(struct sock *sk, struct sk_buff *skb, int err,
 {
 	if (ip_hdr(skb)->version == IPVERSION)
 		return ip_icmp_error(sk, skb, err, port, info, payload);
-	return ipv6_icmp_error(sk, skb, err, port, info, payload);
+	if (IS_ENABLED(CONFIG_AF_RXRPC_IPV6))
+		return ipv6_icmp_error(sk, skb, err, port, info, payload);
 }
 
 /*