This change is for enabling the pppd for vpn authentication and setup.

This change is for enabling the pppd for vpn authentication and setup.
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.