[package] netifd: repair dhcp client id option

Busybox udhcpc dropped support for the -c option, instead it can be emulated by using -x 0x3d:id,
change the dhcp protocol script accordingly and filter all colons from the id while we're at it.
This change supersedes http://patchwork.openwrt.org/patch/1810/

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@32573 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/netifd/files/lib/netifd/proto/dhcp.sh

@@ -35,7 +35,7 @@ proto_dhcp_setup() {
 		-f -t 0 -i "$iface" \
 		${ipaddr:+-r $ipaddr} \
 		${hostname:+-H $hostname} \
-		${clientid:+-c $clientid} \
+		${clientid:+-x 0x3d:${clientid//:/}} \
 		${vendorid:+-V $vendorid} \
 		$broadcast $dhcpopts
 }