network: Use MAC address as DHCP client ID

_systemd-networkd_ uses a randomly-generated ID as the DHCP client
identifier by default.  On Aimee OS, it is not able to persist this ID
between boots; I think it may derive the value from the machine ID.  To
avoid getting a new IP address every boot, we can configure it to use
the MAC address of the device as the DHCP client ID.

overlay/etc/systemd/network/95-default.network

@@ -5,6 +5,7 @@ Type=ether wlan
 DHCP=yes
 
 [DHCPv4]
+ClientIdentifier=mac
 UseDomains=yes
 
 [DHCPv6]