netlink: revert broken, broken "2-clause nla_ok()"

Commit 4f7df33
"netlink: 2-clause nla_ok()" is BROKEN.

First clause tests if "->nla_len" could even be accessed at all,
it can not possibly be omitted.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -698,7 +698,8 @@ static inline int nla_len(const struct nlattr *nla)
  */
 static inline int nla_ok(const struct nlattr *nla, int remaining)
 {
-	return nla->nla_len >= sizeof(*nla) &&
+	return remaining >= (int) sizeof(*nla) &&
+	       nla->nla_len >= sizeof(*nla) &&
 	       nla->nla_len <= remaining;
 }