net: cosmetic: Make the MAC address string less magical

In u-boot printf has been extended with the %pM formatter to allow
printing of MAC addresses. However buffers that want to store a MAC
address cannot safely get the size. Add a define for this case so the
string of a MAC address can be reliably obtained.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/net.h

@@ -40,6 +40,11 @@
 
 /* ARP hardware address length */
 #define ARP_HLEN 6
+/*
+ * The size of a MAC address in string form, each digit requires two chars
+ * and five separator characters to form '00:00:00:00:00:00'.
+ */
+#define ARP_HLEN_ASCII (ARP_HLEN * 2) + (ARP_HLEN - 1)
 
 /* IPv4 addresses are always 32 bits in size */
 struct in_addr {

net/eth_common.c

@@ -32,7 +32,7 @@ int eth_getenv_enetaddr(const char *name, uchar *enetaddr)
 
 int eth_setenv_enetaddr(const char *name, const uchar *enetaddr)
 {
-	char buf[20];
+	char buf[ARP_HLEN_ASCII + 1];
 
 	sprintf(buf, "%pM", enetaddr);