rp-pppoe: Add version 3.8.

rp-pppoe: Add version 3.8.
* The source for version 3.5 hasn't been available for a long time.
* Make sure pppoe is installed suid root.
* Always try to reconnect, pppd handles stop/starting pppoe. This prevents
  lots of annoying problems with pppoe totally giving up (debian patch)
* Accept PPPoE packets from multicast addresses (debian patch)
* Don't check the version of the hosts ppp, we don't support the older
  versions of ppp anyway so just remove those checks.
* RDEPEND on ppp, which is needed to use pppoe
* Hard code pppd and id paths, don't search for them on the host system.