Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Add u3g ppp.conf entry. It provides some starting point to making
use of u3g(4) dongles, and in many cases can work out of the box.

Reviewed by: hselasky
Approved by: re (gjb)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D16974

Revert r301137 and r301163, and implement a correct fix
for the CONFS issue with dma.conf and ppp.conf.

Thank you very much to Bryan Drewery for looking into the
problem and providing this fix.

Pointyhat: gjb
Sponsored by: The FreeBSD Foundation

Move ppp.conf into the ppp sources