ppp: clean up endianness conversions

sparse complains about some harmless endianness issues:

> drivers/net/ppp/pptp.c:281:21: warning: incorrect type in assignment (different base types)
> drivers/net/ppp/pptp.c:281:21: expected unsigned int [usertype] ack
> drivers/net/ppp/pptp.c:281:21: got restricted __be32
> drivers/net/ppp/pptp.c:283:23: warning: cast to restricted __be32

Here 'ack' is assigned a value in network-order, and then also the
byte-swapped value in host-order. Clean this up by doing the byte-swap
as part of the assignment.

> drivers/net/ppp/pptp.c:358:26: warning: cast from restricted __be16
> drivers/net/ppp/pptp.c:358:26: warning: incorrect type in argument 1 (different base types)
> drivers/net/ppp/pptp.c:358:26: expected unsigned short [usertype] call_id
> drivers/net/ppp/pptp.c:358:26: got restricted __be16 [usertype]

Here we use the wrong flavour of byte-swap. Use ntohs(), which of course
gives the same result.

Cc: Dmitry Kozlov <[e-mail]>
Signed-off-by: Julian Wiedmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ppp/pptp.c

···
 		header = (struct pptp_gre_header *)(skb->data);
 
 		/* ack in different place if S = 0 */
-		ack = GRE_IS_SEQ(header->gre_hd.flags) ? header->ack : header->seq;
-
-		ack = ntohl(ack);
-
+		ack = GRE_IS_SEQ(header->gre_hd.flags) ? ntohl(header->ack) :
+							 ntohl(header->seq);
 		if (ack > opt->ack_recv)
 			opt->ack_recv = ack;
 		/* also handle sequence number wrap-around  */
···
 		/* if invalid, discard this packet */
 		goto drop;
 
-	po = lookup_chan(htons(header->call_id), iph->saddr);
+	po = lookup_chan(ntohs(header->call_id), iph->saddr);
 	if (po) {
 		skb_dst_drop(skb);
 		nf_reset_ct(skb);