genetlink: mark families as __ro_after_init

Now genl_register_family() is the only thing (other than the
users themselves, perhaps, but I didn't find any doing that)
writing to the family struct.

In all families that I found, genl_register_family() is only
called from __init functions (some indirectly, in which case
I've add __init annotations to clarifly things), so all can
actually be marked __ro_after_init.

This protects the data structure from accidental corruption.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fou.c

@@ -824,7 +824,7 @@ static const struct genl_ops fou_nl_ops[] = {
 	},
 };
 
-static struct genl_family fou_nl_family = {
+static struct genl_family fou_nl_family __ro_after_init = {
 	.hdrsize	= 0,
 	.name		= FOU_GENL_NAME,
 	.version	= FOU_GENL_VERSION,

net/ipv4/tcp_metrics.c

@@ -1109,7 +1109,7 @@ static const struct genl_ops tcp_metrics_nl_ops[] = {
 	},
 };
 
-static struct genl_family tcp_metrics_nl_family = {
+static struct genl_family tcp_metrics_nl_family __ro_after_init = {
 	.hdrsize	= 0,
 	.name		= TCP_METRICS_GENL_NAME,
 	.version	= TCP_METRICS_GENL_VERSION,