[Cooker] ppp is not ipv6 enabled

[Teemu Torma]

I noticed that ppp is not compiled with ipv6 in 9.1 nor cooker.  Just 
enabling it in pppd/Makefile.linux compiles just fine and seems to work 
as well (I am using adsl via nerim.net).

Any particular reason not to enable it by default?

Teemu