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This change updates the Android specific changes for BoringSSL, which is
Google's cleaned up version of OpenSSL. The change also works with the
current OpenSSL in Android.

Significant changes:
  * Removal of wrapper functions for the OpenSSL hash functions – these
    aren't needed.
  * Use of the OpenSSL DES API. The code currently uses the SSLeay DES
    functions which are supported by current OpenSSL but were deprecated
    sometime in the 1990's. The OpenSSL DES API is the supported API for
    both OpenSSL and the only API in BoringSSL.

    This change has been proposed upstream in
    https://github.com/paulusmack/ppp/pull/24.

Change-Id: I06c87ae4b5175a268739300eab59d65ddac8a2cc

This change syncs external/ppp with upstream. Specifically it's based on
upstream's 6e8eaa7a78b31cdab2edf140a9c8afdb02ffaca5.

In order to do this without blowing away the Android-specific changes, I
ran a script to try and find a matching revision in upstream's git tree
to the initial commit in external/ppp.

Based on the contents of *.c and *.h files in pppd/, upstream's
f8583676904957554c5a8bd14ede415688835f6c matches with the local revision
82c907af.

I diffed upstream's f8583676 with upstream's HEAD and removed chunks
from the result that applied to files that aren't present in Android. In
some places, the diff didn't apply cleanly because of Android-specific
changes:

  1) Local change 8ad0dd2a added two "return UPAP_AUTHNAK;" statements
     in "#if 1" blocks in auth.c. They have been reflected into
     session.c/session_start by always returning SESSION_FAILED.
     (Additionally, new code to query the local password db has been
     disabled via #if !defined(__ANDROID__).)

  2) Upstream now always defines INET6 for Linux so I've pulled IPv6
     support in. (Otherwise sys-linux.c has compile errors.)

  3) linux/ipv6_route.h needed to be included explicitly.

  4) I defined HAVE_LOGWTMP to avoid calling some wtmp functions that
     aren't implemented in Android. A dummy logwtmp is defined.

All the above changes are in __ANDROID__ tags to highlight them.
Additionally I've ensured that all the pre-existing changes are also now
in __ANDROID__ tags.

Change-Id: Ia5abe677d6ba4d5e9f4fbcd4fa03d8911b8bed12

It includes:
  1. Enable the CHAPMS authentication for talking to MS vpn server.
  2. Reuse the message digest/hashing functions in openssl instead of
     the md4, md5 and sha1 functions in the package to save the space.
  3. Enable the execution the ip-up/ip-down script on Android.

Update: add comment and replace tab with spaces.