pppox: remove sk_pppox() helper

The sk member can be directly accessed from struct pppox_sock without
relying on type casting. Remove the sk_pppox() helper and update all
call sites to use po->sk directly.

Signed-off-by: Qingfang Deng <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ppp/pppoe.c

···
 	struct pppox_sock *po;
 
 	po = __get_item(pn, sid, addr, ifindex);
-	if (po && !refcount_inc_not_zero(&sk_pppox(po)->sk_refcnt))
+	if (po && !refcount_inc_not_zero(&po->sk.sk_refcnt))
 		po = NULL;
 
 	return po;
···
 			if (!po)
 				break;
 
-			sk = sk_pppox(po);
+			sk = &po->sk;
 
 			/* We always grab the socket lock, followed by the
 			 * hash_lock, in that order.  Since we should hold the
···
 	if (!po)
 		goto drop;
 
-	return __sk_receive_skb(sk_pppox(po), skb, 0, 1, false);
+	return __sk_receive_skb(&po->sk, skb, 0, 1, false);
 
 drop:
 	kfree_skb(skb);
···
 {
 	struct pppox_sock *po = container_of(work, struct pppox_sock,
 					     proto.pppoe.padt_work);
-	struct sock *sk = sk_pppox(po);
+	struct sock *sk = &po->sk;
 
 	lock_sock(sk);
 	if (po->pppoe_dev) {
···
 	po = get_item(pn, ph->sid, eth_hdr(skb)->h_source, dev->ifindex);
 	if (po)
 		if (!schedule_work(&po->proto.pppoe.padt_work))
-			sock_put(sk_pppox(po));
+			sock_put(&po->sk);
 
 abort:
 	kfree_skb(skb);

drivers/net/ppp/pptp.c

···
 		if (opt->dst_addr.sin_addr.s_addr != s_addr)
 			sock = NULL;
 		else
-			sock_hold(sk_pppox(sock));
+			sock_hold(&sock->sk);
 	}
 	rcu_read_unlock();
 
···
 	struct iphdr  *iph;
 	int    max_headroom;
 
-	if (sk_pppox(po)->sk_state & PPPOX_DEAD)
+	if (po->sk.sk_state & PPPOX_DEAD)
 		goto tx_drop;
 
 	rt = pptp_route_output(po, &fl4);
···
 	if (po) {
 		skb_dst_drop(skb);
 		nf_reset_ct(skb);
-		return sk_receive_skb(sk_pppox(po), skb, 0);
+		return sk_receive_skb(&po->sk, skb, 0);
 	}
 drop:
 	kfree_skb(skb);

include/linux/if_pppox.h

···
 	return (struct pppox_sock *)sk;
 }
 
-static inline struct sock *sk_pppox(struct pppox_sock *po)
-{
-	return (struct sock *)po;
-}
-
 struct module;
 
 struct pppox_proto {