plip: avoid rcu debug splat

WARNING: suspicious RCU usage
5.2.0-rc2-00605-g2638eb8b #1 Not tainted
drivers/net/plip/plip.c:1110 suspicious rcu_dereference_check() usage!

plip_open is called with RTNL held, switch to the correct helper.

Fixes: 2638eb8b ("net: ipv4: provide __rcu annotation for ifa_list")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20220807115304.13257-1-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/plip/plip.c

@@ -1111,7 +1111,7 @@ plip_open(struct net_device *dev)
 		/* Any address will do - we take the first. We already
 		   have the first two bytes filled with 0xfc, from
 		   plip_init_dev(). */
-		const struct in_ifaddr *ifa = rcu_dereference(in_dev->ifa_list);
+		const struct in_ifaddr *ifa = rtnl_dereference(in_dev->ifa_list);
 		if (ifa != NULL) {
 			dev_addr_mod(dev, 2, &ifa->ifa_local, 4);
 		}