net/ipv4/route.c: fix build error

fix:

net/ipv4/route.c: In function 'ip_static_sysctl_init':
net/ipv4/route.c:3225: error: 'ipv4_route_path' undeclared (first use in this function)
net/ipv4/route.c:3225: error: (Each undeclared identifier is reported only once
net/ipv4/route.c:3225: error: for each function it appears in.)
net/ipv4/route.c:3225: error: 'ipv4_route_table' undeclared (first use in this function)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -3222,7 +3222,9 @@ int __init ip_rt_init(void)
  */
 void __init ip_static_sysctl_init(void)
 {
+#ifdef CONFIG_SYSCTL
 	register_sysctl_paths(ipv4_route_path, ipv4_route_table);
+#endif
 }
 
 EXPORT_SYMBOL(__ip_select_ident);