ipv4: Avoid overhead when no custom FIB rules are installed.

If the user hasn't actually installed any custom rules, or fiddled
with the default ones, don't go through the whole FIB rules layer.

It's just pure overhead.

Instead do what we do with CONFIG_IP_MULTIPLE_TABLES disabled, check
the individual tables by hand, one by one.

Also, move fib_num_tclassid_users into the ipv4 network namespace.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 227f0cd..599e48f 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -11,6 +11,7 @@
 struct ipv4_devconf;
 struct fib_rules_ops;
 struct hlist_head;
+struct fib_table;
 struct sock;
 
 struct netns_ipv4 {
@@ -24,6 +25,13 @@
 	struct ipv4_devconf	*devconf_dflt;
 #ifdef CONFIG_IP_MULTIPLE_TABLES
 	struct fib_rules_ops	*rules_ops;
+	bool			fib_has_custom_rules;
+	struct fib_table	*fib_local;
+	struct fib_table	*fib_main;
+	struct fib_table	*fib_default;
+#endif
+#ifdef CONFIG_IP_ROUTE_CLASSID
+	int			fib_num_tclassid_users;
 #endif
 	struct hlist_head	*fib_table_hash;
 	struct sock		*fibnl;