phonet: fix rtm_phonet_notify() skb allocation

fill_route() stores three components in the skb:

- struct rtmsg
- RTA_DST (u8)
- RTA_OIF (u32)

Therefore, rtm_phonet_notify() should use

NLMSG_ALIGN(sizeof(struct rtmsg)) +
nla_total_size(1) +
nla_total_size(4)

Fixes: f062f41 ("Phonet: routing table Netlink interface")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Rémi Denis-Courmont <courmisch@gmail.com>
Link: https://lore.kernel.org/r/20240502161700.1804476-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/phonet/pn_netlink.c

@@ -193,7 +193,7 @@ void rtm_phonet_notify(int event, struct net_device *dev, u8 dst)
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
+	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct rtmsg)) +
 			nla_total_size(1) + nla_total_size(4), GFP_KERNEL);
 	if (skb == NULL)
 		goto errout;