bareudp: use ipv6_mod_enabled to check if IPv6 enabled

bareudp_create_sock() use AF_INET6 by default if IPv6 CONFIG enabled.
But if user start kernel with ipv6.disable=1, the bareudp sock will
created failed, which cause the interface open failed even with ethertype
ip. e.g.

 # ip link add bareudp1 type bareudp dstport 2 ethertype ip
 # ip link set bareudp1 up
 RTNETLINK answers: Address family not supported by protocol

Fix it by using ipv6_mod_enabled() to check if IPv6 enabled. There is
no need to check IS_ENABLED(CONFIG_IPV6) as ipv6_mod_enabled() will
return false when CONFIG_IPV6 no enabled in include/linux/ipv6.h.
Reported-by: Jianlin Shi <jishi@redhat.com>
Fixes: 571912c6 ("net: UDP tunnel encapsulation module for tunnelling different protocols like MPLS, IP, NSH etc.")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20220315062618.156230-1-liuhangbin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/bareudp.c

@@ -148,14 +148,14 @@ static int bareudp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
 	skb_reset_network_header(skb);
 	skb_reset_mac_header(skb);
 
-	if (!IS_ENABLED(CONFIG_IPV6) || family == AF_INET)
+	if (!ipv6_mod_enabled() || family == AF_INET)
 		err = IP_ECN_decapsulate(oiph, skb);
 	else
 		err = IP6_ECN_decapsulate(oiph, skb);
 
 	if (unlikely(err)) {
 		if (log_ecn_error) {
-			if  (!IS_ENABLED(CONFIG_IPV6) || family == AF_INET)
+			if  (!ipv6_mod_enabled() || family == AF_INET)
 				net_info_ratelimited("non-ECT from %pI4 "
 						     "with TOS=%#x\n",
 						     &((struct iphdr *)oiph)->saddr,
@@ -221,11 +221,12 @@ static struct socket *bareudp_create_sock(struct net *net, __be16 port)
 	int err;
 
 	memset(&udp_conf, 0, sizeof(udp_conf));
-#if IS_ENABLED(CONFIG_IPV6)
-	udp_conf.family = AF_INET6;
-#else
-	udp_conf.family = AF_INET;
-#endif
+
+	if (ipv6_mod_enabled())
+		udp_conf.family = AF_INET6;
+	else
+		udp_conf.family = AF_INET;
+
 	udp_conf.local_udp_port = port;
 	/* Open UDP socket */
 	err = udp_sock_create(net, &udp_conf, &sock);
@@ -448,7 +449,7 @@ static netdev_tx_t bareudp_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	rcu_read_lock();
-	if (IS_ENABLED(CONFIG_IPV6) && info->mode & IP_TUNNEL_INFO_IPV6)
+	if (ipv6_mod_enabled() && info->mode & IP_TUNNEL_INFO_IPV6)
 		err = bareudp6_xmit_skb(skb, dev, bareudp, info);
 	else
 		err = bareudp_xmit_skb(skb, dev, bareudp, info);
@@ -478,7 +479,7 @@ static int bareudp_fill_metadata_dst(struct net_device *dev,
 
 	use_cache = ip_tunnel_dst_cache_usable(skb, info);
 
-	if (!IS_ENABLED(CONFIG_IPV6) || ip_tunnel_info_af(info) == AF_INET) {
+	if (!ipv6_mod_enabled() || ip_tunnel_info_af(info) == AF_INET) {
 		struct rtable *rt;
 		__be32 saddr;