net: Add new wol command - Wake on LAN

Add a new command 'wol': Wait for an incoming Wake-on-LAN packet or
time out if no WoL packed is received.
If the WoL packet contains a password, it is saved in the environment
variable 'wolpassword' using the etherwake format (dot or colon
separated decimals).

Intended use case: a networked device should boot an alternate image.
It's attached to a network on a client site, modifying the DHCP server
configuration or setup of a tftp server is not allowed.
After power on the device waits a few seconds for a WoL packet. If a
packet is received, the device boots the alternate image. Otherwise
it boots the default image.

This method is a simple way to interact with a system via network even
if only the MAC address is known. Tools to send WoL packets are
available on all common platforms.

Some Ethernet drivers seem to pad the incoming packet. The additional
padding bytes might be recognized as Wake-on-LAN password bytes.

By default enabled in pengwyn_defconfig.

Signed-off-by: Lothar Felten <lothar.felten@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/include/net.h b/include/net.h
index 5760685..9c7199a 100644
--- a/include/net.h
+++ b/include/net.h
@@ -344,6 +344,7 @@
 
 #define PROT_IP		0x0800		/* IP protocol			*/
 #define PROT_ARP	0x0806		/* IP ARP protocol		*/
+#define PROT_WOL	0x0842		/* ether-wake WoL protocol	*/
 #define PROT_RARP	0x8035		/* IP ARP protocol		*/
 #define PROT_VLAN	0x8100		/* IEEE 802.1q protocol		*/
 #define PROT_IPV6	0x86dd		/* IPv6 over bluebook		*/
@@ -535,7 +536,7 @@
 
 enum proto_t {
 	BOOTP, RARP, ARP, TFTPGET, DHCP, PING, DNS, NFS, CDP, NETCONS, SNTP,
-	TFTPSRV, TFTPPUT, LINKLOCAL, FASTBOOT
+	TFTPSRV, TFTPPUT, LINKLOCAL, FASTBOOT, WOL
 };
 
 extern char	net_boot_file_name[1024];/* Boot File name */