netfilter: xt_socket: missing ifdef CONFIG_IP6_NF_IPTABLES dependency

nf_defrag_ipv6_disable() requires CONFIG_IP6_NF_IPTABLES.

Fixes: 75063c9294 ("netfilter: xt_socket: fix a typo in socket_mt_destroy()")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Eric Dumazet<edumazet@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_socket.c

@@ -220,8 +220,10 @@ static void socket_mt_destroy(const struct xt_mtdtor_param *par)
 {
 	if (par->family == NFPROTO_IPV4)
 		nf_defrag_ipv4_disable(par->net);
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
 	else if (par->family == NFPROTO_IPV6)
 		nf_defrag_ipv6_disable(par->net);
+#endif
 }
 
 static struct xt_match socket_mt_reg[] __read_mostly = {