Change module debian_ip.py for support PPPoE.

Hello. I added support PPPoE connection for debian os. I can use salt.states.network for install pppoe connection, example:
<pre>
dsl-provider:
  network.managed:
    - enabled: True
    - type: pppoe
    - proto: ppp
    - user: user
    - password: password
    - pppoe_iface: eth0
    - provider: dsl-provider
</pre>
Will you be able to add my changes? Thanks!