ipv6: propagate ipv6_add_dev's error returns out of ipv6_find_idev

Currently, ipv6_find_idev returns NULL when ipv6_add_dev fails,
ignoring the specific error value. This results in addrconf_add_dev
returning ENOBUFS in all cases, which is unfortunate in cases such as:

    # ip link add dummyX type dummy
    # ip link set dummyX mtu 1200 up
    # ip addr add 2000::/64 dev dummyX
    RTNETLINK answers: No buffer space available

Commit a317a2f1 ("ipv6: fail early when creating netdev named all
or default") introduced error returns in ipv6_add_dev. Before that,
that function would simply return NULL for all failures.
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -478,7 +478,7 @@ static struct inet6_dev *ipv6_find_idev(struct net_device *dev)
 	if (!idev) {
 		idev = ipv6_add_dev(dev);
 		if (IS_ERR(idev))
-			return NULL;
+			return idev;
 	}
 
 	if (dev->flags&IFF_UP)
@@ -2466,8 +2466,8 @@ static struct inet6_dev *addrconf_add_dev(struct net_device *dev)
 	ASSERT_RTNL();
 
 	idev = ipv6_find_idev(dev);
-	if (!idev)
-		return ERR_PTR(-ENOBUFS);
+	if (IS_ERR(idev))
+		return idev;
 
 	if (idev->cnf.disable_ipv6)
 		return ERR_PTR(-EACCES);
@@ -3159,7 +3159,7 @@ static void init_loopback(struct net_device *dev)
 	ASSERT_RTNL();
 
 	idev = ipv6_find_idev(dev);
-	if (!idev) {
+	if (IS_ERR(idev)) {
 		pr_debug("%s: add_dev failed\n", __func__);
 		return;
 	}
@@ -3374,7 +3374,7 @@ static void addrconf_sit_config(struct net_device *dev)
 	 */
 
 	idev = ipv6_find_idev(dev);
-	if (!idev) {
+	if (IS_ERR(idev)) {
 		pr_debug("%s: add_dev failed\n", __func__);
 		return;
 	}
@@ -3399,7 +3399,7 @@ static void addrconf_gre_config(struct net_device *dev)
 	ASSERT_RTNL();
 
 	idev = ipv6_find_idev(dev);
-	if (!idev) {
+	if (IS_ERR(idev)) {
 		pr_debug("%s: add_dev failed\n", __func__);
 		return;
 	}
@@ -4773,8 +4773,8 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			 IFA_F_MCAUTOJOIN | IFA_F_OPTIMISTIC;
 
 	idev = ipv6_find_idev(dev);
-	if (!idev)
-		return -ENOBUFS;
+	if (IS_ERR(idev))
+		return PTR_ERR(idev);
 
 	if (!ipv6_allow_optimistic_dad(net, idev))
 		cfg.ifa_flags &= ~IFA_F_OPTIMISTIC;