[IPV6]: Sparse: Declare non-static ipv6_{route,icmp,frag}_sysctl_init() in header.

Fix the following sparse warnings:
| net/ipv6/route.c:2491:18: warning: symbol 'ipv6_route_sysctl_init' was not declared. Should it be static?
| net/ipv6/icmp.c:922:18: warning: symbol 'ipv6_icmp_sysctl_init' was not declared. Should it be static?
| net/ipv6/reassembly.c:628:6: warning: symbol 'ipv6_frag_sysctl_init' was not declared. Should it be static?
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

include/net/ipv6.h

@@ -586,6 +586,10 @@ extern int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
 			 int __user *optlen);
 
 #ifdef CONFIG_PROC_FS
+extern struct ctl_table *ipv6_icmp_sysctl_init(struct net *net);
+extern void ipv6_frag_sysctl_init(struct net *net);
+extern struct ctl_table *ipv6_route_sysctl_init(struct net *net);
+
 extern int  ac6_proc_init(void);
 extern void ac6_proc_exit(void);
 extern int  raw6_proc_init(void);

net/ipv6/af_inet6.c

@@ -72,8 +72,6 @@ MODULE_LICENSE("GPL");
 static struct list_head inetsw6[SOCK_MAX];
 static DEFINE_SPINLOCK(inetsw6_lock);
 
-void ipv6_frag_sysctl_init(struct net *net);
-
 static __inline__ struct ipv6_pinfo *inet6_sk_generic(struct sock *sk)
 {
 	const int offset = sk->sk_prot->obj_size - sizeof(struct ipv6_pinfo);

net/ipv6/sysctl_net_ipv6.c

@@ -14,9 +14,6 @@
 #include <net/addrconf.h>
 #include <net/inet_frag.h>
 
-extern struct ctl_table *ipv6_route_sysctl_init(struct net *net);
-extern struct ctl_table *ipv6_icmp_sysctl_init(struct net *net);
-
 static ctl_table ipv6_table_template[] = {
 	{
 		.ctl_name	= NET_IPV6_ROUTE,