A deep analysis of simultaneously running timers showed we can use a
slightly smaller value for PPP_NUM_TIMEOUTS_PER_PCB, value which was
arbitrarily chosen to a safe value based on the number of enabled PPP
features. Add the boring and long analysis to the end of our internal
header file and use the result in ppp_opts.h.
Signed-off-by: Sylvain Rochet <gradator@gradator.net>