[NET]: Fix sparse warnings

Of this type, mostly:

CHECK   net/ipv6/netfilter.c
net/ipv6/netfilter.c:96:12: warning: symbol 'ipv6_netfilter_init' was not declared. Should it be static?
net/ipv6/netfilter.c:101:6: warning: symbol 'ipv6_netfilter_fini' was not declared. Should it be static?

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
index d594288..1418388 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1370,4 +1370,16 @@
 }
 #endif
 
+extern void sk_init(void);
+
+#ifdef CONFIG_SYSCTL
+extern struct ctl_table core_table[];
+extern int sysctl_optmem_max;
+#endif
+
+#ifdef CONFIG_PROC_FS
+extern __u32 sysctl_wmem_default;
+extern __u32 sysctl_rmem_default;
+#endif
+
 #endif	/* _SOCK_H */