ethtool: mark netlink family as __ro_after_init

Like all genl families ethtool_genl_family needs to not
be a straight up constant, because it's modified/initialized
by genl_register_family(). After init, however, it's only
passed to genlmsg_put() & co. therefore we can mark it
as __ro_after_init.

Since genl_family structure contains function pointers
mark this as a fix.

Fixes: 2b4a8990 ("ethtool: introduce ethtool netlink interface")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/netlink.c

@@ -866,7 +866,7 @@ static const struct genl_multicast_group ethtool_nl_mcgrps[] = {
 	[ETHNL_MCGRP_MONITOR] = { .name = ETHTOOL_MCGRP_MONITOR_NAME },
 };
 
-static struct genl_family ethtool_genl_family = {
+static struct genl_family ethtool_genl_family __ro_after_init = {
 	.name		= ETHTOOL_GENL_NAME,
 	.version	= ETHTOOL_GENL_VERSION,
 	.netnsok	= true,