PPP: Port to the new stack.

Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>

This is a squash of the 42 commits by @mshlyn, as I couldn't find a
way to break them into logical chunks. I did not include these in the build,
as it appears that they only partially work anyway, and much more cleanup is
still needed. However, this is a huge improvement on what was in the tree
before, which looked horrendous and didn't even compile (as it was designed
for the old stack).

Mostly fixes #812.