networkd-config: force ipv4 clientid to 'mac'

Traditionally the DHCP clients will send the ethernet
MAC address as the 'ClientID' in the DHCP request.

DHCP on IPv6 introduced a new identifier called a DUID
as the primary system identifier that is sent to the DHCP
server.  This was also added back to IPv4 via RFC 4361
and is the default in systemd-networkd.

Some legacy system installations do not support DUIDs
and as a short-term fix, we will force 'mac' to be used
instead of 'duid'.  See openbmc/openbmc#1280 for long-term
discussion.

Fixes openbmc/openbmc#1272.

Change-Id: Idd46c08071b51ad8d1f40f43efade98c9c030dea
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/netman.py b/netman.py
index 99984d0..230cb5e 100755
--- a/netman.py
+++ b/netman.py
@@ -309,6 +309,8 @@
         networkconf.write ('Name=' + (device) + '\n')
         networkconf.write ('[Network]' + '\n')
         networkconf.write ('DHCP=yes')
+        networkconf.write ('[DHCP]' + '\n')
+        networkconf.write ('ClientIdentifier=mac' + '\n')
         networkconf.close ()
 
         print("Restarting networkd service...")