change dtmf vol to 13

src/switch_rtp.c

@@ -3881,7 +3881,7 @@ static void do_2833(switch_rtp_t *rtp_session)
 			rtp_session->dtmf_data.out_digit_dur = rdigit->duration;
 			rtp_session->dtmf_data.out_digit = rdigit->digit;
 			rtp_session->dtmf_data.out_digit_packet[0] = (unsigned char) switch_char_to_rfc2833(rdigit->digit);
-			rtp_session->dtmf_data.out_digit_packet[1] = 7;
+			rtp_session->dtmf_data.out_digit_packet[1] = 13;
 			rtp_session->dtmf_data.out_digit_packet[2] = (unsigned char) (rtp_session->dtmf_data.out_digit_sub_sofar >> 8);
 			rtp_session->dtmf_data.out_digit_packet[3] = (unsigned char) rtp_session->dtmf_data.out_digit_sub_sofar;