net: kill an RCU warning in inet_fill_link_af()

commits 9f0f727 (ipv4: AF_INET link address family) and cf7afbf
(rtnl: make link af-specific updates atomic) used incorrect
__in_dev_get_rcu() in RTNL protected contexts, triggering PROVE_RCU
warnings.

Switch to __in_dev_get_rtnl(), wich is more appropriate, since we hold
RTNL.

Based on a report and initial patch from Amerigo Wang.

Reported-by: Amerigo Wang <amwang@redhat.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Thomas Graf <tgraf@infradead.org>
Reviewed-by: WANG Cong <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -1258,7 +1258,7 @@ static void rtmsg_ifa(int event, struct in_ifaddr *ifa, struct nlmsghdr *nlh,
 
 static size_t inet_get_link_af_size(const struct net_device *dev)
 {
-	struct in_device *in_dev = __in_dev_get_rcu(dev);
+	struct in_device *in_dev = __in_dev_get_rtnl(dev);
 
 	if (!in_dev)
 		return 0;
@@ -1268,7 +1268,7 @@ static size_t inet_get_link_af_size(const struct net_device *dev)
 
 static int inet_fill_link_af(struct sk_buff *skb, const struct net_device *dev)
 {
-	struct in_device *in_dev = __in_dev_get_rcu(dev);
+	struct in_device *in_dev = __in_dev_get_rtnl(dev);
 	struct nlattr *nla;
 	int i;
 
@@ -1295,7 +1295,7 @@ static int inet_validate_link_af(const struct net_device *dev,
 	struct nlattr *a, *tb[IFLA_INET_MAX+1];
 	int err, rem;
 
-	if (dev && !__in_dev_get_rcu(dev))
+	if (dev && !__in_dev_get_rtnl(dev))
 		return -EAFNOSUPPORT;
 
 	err = nla_parse_nested(tb, IFLA_INET_MAX, nla, inet_af_policy);
@@ -1319,7 +1319,7 @@ static int inet_validate_link_af(const struct net_device *dev,
 
 static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla)
 {
-	struct in_device *in_dev = __in_dev_get_rcu(dev);
+	struct in_device *in_dev = __in_dev_get_rtnl(dev);
 	struct nlattr *a, *tb[IFLA_INET_MAX+1];
 	int rem;