Correct two bugs that may result in incorrect CBCP response for

Correct two bugs that may result in incorrect CBCP response for
administrator specified number.

The implementation in our version transmits extra zero byte that is a
violation of the Microsoft PPP Callback Control Protocol section 3.2[1].
This can lead to incorrect behavior on certain devices, as reported
in bin/50613.

Confirmed with: cbcp.c in ppp's cvs, rev. 1.4 and 1.15 [2]

Submitted-by: Xin LI <delphij@frontfree.net>
Taken-From: FreeBSD/rev1.7
Submitted-to-FreeBSD-by: Dmitry Pryanishnikov <dmitry at atlantis.dp.ua>
PR: FreeBSD:bin/50613