vxlan: correctly handle ipv6.disable module parameter

BugLink: https://bugs.launchpad.net/bugs/1771301

When IPv6 is compiled but disabled at runtime, __vxlan_sock_add returns
-EAFNOSUPPORT. For metadata based tunnels, this causes failure of the whole
operation of bringing up the tunnel.

Ignore failure of IPv6 socket creation for metadata based tunnels caused by
IPv6 not being available.

Fixes: b1be00a6 ("vxlan: support both IPv4 and IPv6 sockets in a single vxlan device")
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(backported from commit d074bf96)
Signed-off-by: Eric Desrochers <eric.desrochers@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

drivers/net/vxlan.c

@@ -2947,17 +2947,21 @@ static int __vxlan_sock_add(struct vxlan_dev *vxlan, bool ipv6)
 
 static int vxlan_sock_add(struct vxlan_dev *vxlan)
 {
-	bool ipv6 = vxlan->flags & VXLAN_F_IPV6;
 	bool metadata = vxlan->flags & VXLAN_F_COLLECT_METADATA;
+	bool ipv6 = vxlan->flags & VXLAN_F_IPV6 || metadata;
+	bool ipv4 = !ipv6 || metadata;
 	int ret = 0;
 
 	vxlan->vn4_sock = NULL;
 #if IS_ENABLED(CONFIG_IPV6)
 	vxlan->vn6_sock = NULL;
-	if (ipv6 || metadata)
+	if (ipv6) {
 		ret = __vxlan_sock_add(vxlan, true);
+		if (ret < 0 && ret != -EAFNOSUPPORT)
+			ipv4 = false;
+	}
 #endif
-	if (!ret && (!ipv6 || metadata))
+	if (ipv4)
 		ret = __vxlan_sock_add(vxlan, false);
 	if (ret < 0)
 		vxlan_sock_release(vxlan);