Work on task #13907 PPP cleanups: Move PPP options from opt.h to dedicated ppp_opts.h file
PPP: fix constness in PPP related files (GCC -Wcast-qual) Signed-off-by: Dirk Ziegelmeier <dirk@ziegelmeier.net>
Moved PPP headers into include/netif/ppp/, fixing bug #37040.