net: decnet: dn_nsp_out: use swap macro in dn_mk_ack_header

Make use of the swap macro and remove unnecessary variable tmp.
This makes the code easier to read and maintain.

This code was detected with the help of Coccinelle.
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/decnet/dn_nsp_out.c

@@ -313,11 +313,8 @@ static __le16 *dn_mk_ack_header(struct sock *sk, struct sk_buff *skb, unsigned c
 	ackcrs |= 0x8000;
 
 	/* If this is an "other data/ack" message, swap acknum and ackcrs */
-	if (other) {
-		unsigned short tmp = acknum;
-		acknum = ackcrs;
-		ackcrs = tmp;
-	}
+	if (other)
+		swap(acknum, ackcrs);
 
 	/* Set "cross subchannel" bit in ackcrs */
 	ackcrs |= 0x2000;