net: rtnetlink: fix error handling in rtnl_fill_statsinfo()

The clang static analyzer reports this issue
rtnetlink.c:5481:2: warning: Undefined or garbage
  value returned to caller
  return err;
  ^~~~~~~~~~

There is a function level err variable, in the
list_for_each_entry_rcu block there is a shadow
err.  Remove the shadow.

In the same block, the call to nla_nest_start_noflag()
can fail without setting an err.  Set the err
to -EMSGSIZE.

Fixes: 216e690631 ("net: rtnetlink: rtnl_fill_statsinfo(): Permit non-EMSGSIZE error returns")
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -5440,12 +5440,12 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
 		list_for_each_entry_rcu(af_ops, &rtnl_af_ops, list) {
 			if (af_ops->fill_stats_af) {
 				struct nlattr *af;
-				int err;
 
 				af = nla_nest_start_noflag(skb,
 							   af_ops->family);
 				if (!af) {
 					rcu_read_unlock();
+					err = -EMSGSIZE;
 					goto nla_put_failure;
 				}
 				err = af_ops->fill_stats_af(skb, dev);