HFP: support pause character "Comma" in acceptable dial digit string

* To avoid bt stack filter MO call initiated from HF end with by sending dial command with modifier character "," (Comma)

Bug: 118401445
Test: making MO call from carkit/equipment by sending ATD command with phone number plus comma plus DTMF digitals
Change-Id: I5acb913a3c034f10ad704c1b8466634df122b580