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/hsr/hsr_netlink.c

@@ -461,7 +461,7 @@ static const struct genl_ops hsr_ops[] = {
 	},
 };
 
-static struct genl_family hsr_genl_family = {
+static struct genl_family hsr_genl_family __ro_after_init = {
 	.hdrsize = 0,
 	.name = "HSR",
 	.version = 1,