DO NOT MERGE Add a new carrier config for DTMF tone gap in CDMA.

Adding a new carrier config key to specify the gap between the DTMF
tones sent out to the network. Setting it to 100ms by default.
This is based on a similar set of changes for IMS calls: ag/747865.

BUG: 19118840
Change-Id: Ifb64fe406509fe7c401ad1c4b4e906d6643e327b
1 file changed