mgw: accept zero-length RTP payload as BFI Mainline OsmoBTS now has an option (rtp continuous-streaming) that causes it to emit an RTP packet every 20 ms without gaps, sending a BFI marker in the form of zero-length RTP payload when it has nothing else to send. These codec-independent BFI markers don't indicate TAF, but this provision is a good start. Accept this BFI packet format in themwi-mgw.

/*
 * Here we implement a function that validates DTMF digits which arrive
 * from GSM MS via MNCC_START_DTMF_IND.
 */

is_valid_dtmf_digit(c)
{
	switch (c) {
	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	case '8':
	case '9':
	case '*':
	case '#':
	case 'A':
	case 'B':
	case 'C':
	case 'D':
		return(1);
	default:
		return(0);
	}
}