Add 'enable-ipv6' option to pppoe connections, needs PPPd to support
ipv6 or this option will break any pppoe connection.
See this commit :
https://github.com/kouak/ppp/commit/481c7120bd08496ae73f8ac96b277fdcf60a55cb
Merge pull request #3 from kouak/lithium

Bug #27: Add 'enable-ipv6' option to pppoe connections