hsr: Handle failures in module init

A failure during registration of the netdev notifier was not handled at
all. A failure during netlink initialization did not unregister the netdev
notifier.

Handle failures of netdev notifier registration and netlink initialization.
Both functions should only return negative values on failure and thereby
lead to the hsr module not being loaded.

Fixes: f421436a ("net/hsr: Add support for the High-availability Seamless Redundancy protocol (HSRv0)")
Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Reviewed-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/3ce097c15e3f7ace98fc7fd9bcbf299f092e63d1.1710504184.git.fmaurer@redhat.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/hsr/hsr_main.c

@@ -148,14 +148,21 @@ static struct notifier_block hsr_nb = {
 
 static int __init hsr_init(void)
 {
-	int res;
+	int err;
 
 	BUILD_BUG_ON(sizeof(struct hsr_tag) != HSR_HLEN);
 
-	register_netdevice_notifier(&hsr_nb);
-	res = hsr_netlink_init();
+	err = register_netdevice_notifier(&hsr_nb);
+	if (err)
+		return err;
+
+	err = hsr_netlink_init();
+	if (err) {
+		unregister_netdevice_notifier(&hsr_nb);
+		return err;
+	}
 
-	return res;
+	return 0;
 }
 
 static void __exit hsr_exit(void)