ipv4: Disallow non-namespace aware protocols to register.

All in-tree ipv4 protocol implementations are now namespace
aware.  Therefore all the run-time checks are superfluous.

Reject registry of any non-namespace aware ipv4 protocol.
Eventually we'll remove prot->netns_ok and this registry
time check as well.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/protocol.c

@@ -37,6 +37,12 @@ const struct net_offload __rcu *inet_offloads[MAX_INET_PROTOS] __read_mostly;
 
 int inet_add_protocol(const struct net_protocol *prot, unsigned char protocol)
 {
+	if (!prot->netns_ok) {
+		pr_err("Protocol %u is not namespace aware, cannot register.\n",
+			protocol);
+		return -EINVAL;
+	}
+
 	return !cmpxchg((const struct net_protocol **)&inet_protos[protocol],
 			NULL, prot) ? 0 : -1;
 }