net: spread __net_init, __net_exit

__net_init/__net_exit are apparently not going away, so use them
to full extent.

In some cases __net_init was removed, because it was called from
__net_exit code.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 4ae661b..217dbc2 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -951,7 +951,7 @@
 	{ },
 };
 
-struct ctl_table *ipv6_icmp_sysctl_init(struct net *net)
+struct ctl_table * __net_init ipv6_icmp_sysctl_init(struct net *net)
 {
 	struct ctl_table *table;