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>
diff --git a/include/linux/genl_magic_func.h b/include/linux/genl_magic_func.h
index 40c2e39..377257d 100644
--- a/include/linux/genl_magic_func.h
+++ b/include/linux/genl_magic_func.h
@@ -293,7 +293,7 @@ static int CONCAT_(GENL_MAGIC_FAMILY, _genl_multicast_ ## group)(	\
 #undef GENL_mc_group
 #define GENL_mc_group(group)
 
-static struct genl_family ZZZ_genl_family __read_mostly = {
+static struct genl_family ZZZ_genl_family __ro_after_init = {
 	.name = __stringify(GENL_MAGIC_FAMILY),
 	.version = GENL_MAGIC_VERSION,
 #ifdef GENL_MAGIC_FAMILY_HDRSZ