dhclient: send client-identifier matching hardware address

Forcing dhclient to use hardware address instead of DUID to make it
predictable and allows system installation in whitelist based networks.

modules.d/40network/dhclient.conf

@@ -1,6 +1,8 @@
 
 option classless-routes code 121 = array of unsigned integer 8;
 
+send dhcp-client-identifier = hardware;
+
 request subnet-mask, broadcast-address, time-offset, routers,
         domain-name, domain-name-servers, domain-search, host-name,
         root-path, interface-mtu, classless-routes;