Add to chan_dahdi ISDN HOLD, Call deflection, and keypad facility support.

Add to chan_dahdi ISDN HOLD, Call deflection, and keypad facility support.

* Added handling of received HOLD/RETRIEVE messages and the optional ability
  to transfer a held call on disconnect similar to an analog phone.
* Added CallRerouting/CallDeflection support for Q.SIG, ETSI PTP, ETSI PTMP.
  Will reroute/deflect an outgoing call when receive the message.
  Can use the DAHDISendCallreroutingFacility to send the message for the
  supported switches.
* Added ability to send/receive keypad digits in the SETUP message.
  Send keypad digits in SETUP message: Dial(DAHDI/g1[/K<keypad_digits>][/extension])
  Access any received keypad digits in SETUP message by: ${CHANNEL(keypad_digits)}
* Added support for BRI PTMP NT mode.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@225692 65c4cc65-6c06-0410-ace0-fbb531ad65f3