netfilter: log_arp: Use ARPHRD_ETHER instead of literal '1'

There is one macro ARPHRD_ETHER which defines the ethernet proto for ARP,
so we could use it instead of the literal number '1'.
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nf_log_arp.c

@@ -62,7 +62,7 @@ static void dump_arp_packet(struct nf_log_buf *m,
 	/* If it's for Ethernet and the lengths are OK, then log the ARP
 	 * payload.
 	 */
-	if (ah->ar_hrd != htons(1) ||
+	if (ah->ar_hrd != htons(ARPHRD_ETHER) ||
 	    ah->ar_hln != ETH_ALEN ||
 	    ah->ar_pln != sizeof(__be32))
 		return;