Add delay between postdial DTMF tones for CDMA.

Adding a delay between the postdial DTMF char tones sent out to the
network for CDMA phones.
This is based on a similar set of changes for IMS calls: ag/747687.

BUG: 19118840
Change-Id: Ifcd70bb44da5fba808f31b3021f063b545a1b740