net/ipv4/arp.c: Use common hex_asc helpers

Here the local hexbuf is a duplicate of global const char hex_asc from
lib/hexdump.c, except the hex letters' cases:

	const char hexbuf[] = "0123456789ABCDEF";

	const char hex_asc[] = "0123456789abcdef";

and here to print HW addresses, the hex cases are not significant.

Thanks to Harvey Harrison to introduce the hex_asc_hi/hex_asc_lo helpers.
Signed-off-by: Denis Cheng <crquan@gmail.com>
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/arp.c

@@ -1288,7 +1288,6 @@ static void arp_format_neigh_entry(struct seq_file *seq,
 				   struct neighbour *n)
 {
 	char hbuffer[HBUFFERLEN];
-	const char hexbuf[] = "0123456789ABCDEF";
 	int k, j;
 	char tbuf[16];
 	struct net_device *dev = n->dev;
@@ -1302,8 +1301,8 @@ static void arp_format_neigh_entry(struct seq_file *seq,
 	else {
 #endif
 	for (k = 0, j = 0; k < HBUFFERLEN - 3 && j < dev->addr_len; j++) {
-		hbuffer[k++] = hexbuf[(n->ha[j] >> 4) & 15];
-		hbuffer[k++] = hexbuf[n->ha[j] & 15];
+		hbuffer[k++] = hex_asc_hi(n->ha[j]);
+		hbuffer[k++] = hex_asc_lo(n->ha[j]);
 		hbuffer[k++] = ':';
 	}
 	hbuffer[--k] = 0;