net: ipmr: make function ipmr_notifier_init static

The function ipmr_notifier_init is local to the source and does
not need to be in global scope, so make it static.

Cleans up sparse warning:
warning: symbol 'ipmr_notifier_init' was not declared. Should it be static?
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -3224,7 +3224,7 @@ static const struct fib_notifier_ops ipmr_notifier_ops_template = {
 	.owner		= THIS_MODULE,
 };
 
-int __net_init ipmr_notifier_init(struct net *net)
+static int __net_init ipmr_notifier_init(struct net *net)
 {
 	struct fib_notifier_ops *ops;