net: Fix CONFIG_SYSCTL ifdef test.

> include/net/ip.h:211:5: warning: "CONFIG_SYSCTL" is not defined [-Wundef]
>  #if CONFIG_SYSCTL
>      ^

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -208,7 +208,7 @@ static inline u64 snmp_fold_field64(void __percpu *mib, int offt, size_t syncp_o
 
 void inet_get_local_port_range(struct net *net, int *low, int *high);
 
-#if CONFIG_SYSCTL
+#ifdef CONFIG_SYSCTL
 static inline int inet_is_local_reserved_port(struct net *net, int port)
 {
 	if (!net->ipv4.sysctl_local_reserved_ports)