PTM is Packet Transfer Mode
VDSL2 interface supports Packet Transfer Mode (PTM). The PTM mode transports packets (IP, PPP, Ethernet, MPLS, and so on) over DSL links as an alternative to using Asynchronous Transfer Mode (ATM). PTM is based on the Ethernet in the First Mile (EFM) IEEE802.3ah standard.
When Adding select ptm0 and select Bridging
you have to bridge the pmt0.1 interface to an Ethernet port ie; eth0.0
This allows DHCP to be picked up directly over the bridge