res_rtp_asterisk: Only raise flash control frame on end.

Flash in RTP is conveyed the same as DTMF, just with a
specific digit. In Asterisk however we do flash as a
single control frame.

This change makes it so that only on end do we provide
the flash control frame to the core. Previously we would
provide a flash control frame on both begin and end,
causing flash to work improperly.

ASTERISK-29373

Change-Id: I1accd9c6e859811336e670e698bd8bd124f33226

res/res_rtp_asterisk.c

@@ -5479,15 +5479,24 @@ static struct ast_frame *create_dtmf_frame(struct ast_rtp_instance *instance, en
 		rtp->resp = 0;
 		rtp->dtmfsamples = 0;
 		return &ast_null_frame;
+	} else if (type == AST_FRAME_DTMF_BEGIN && rtp->resp == 'X') {
+		ast_debug_rtp(1, "(%p) RTP ignore flash begin from '%s'\n",
+			instance, ast_sockaddr_stringify(&remote_address));
+		rtp->resp = 0;
+		rtp->dtmfsamples = 0;
+		return &ast_null_frame;
 	}
-	ast_debug_rtp(1, "(%p) RTP creating %s DTMF Frame: %d (%c), at %s\n",
-		instance, type == AST_FRAME_DTMF_END ? "END" : "BEGIN",
-		rtp->resp, rtp->resp,
-		ast_sockaddr_stringify(&remote_address));
+
 	if (rtp->resp == 'X') {
+		ast_debug_rtp(1, "(%p) RTP creating flash Frame at %s\n",
+			instance, ast_sockaddr_stringify(&remote_address));
 		rtp->f.frametype = AST_FRAME_CONTROL;
 		rtp->f.subclass.integer = AST_CONTROL_FLASH;
 	} else {
+		ast_debug_rtp(1, "(%p) RTP creating %s DTMF Frame: %d (%c), at %s\n",
+			instance, type == AST_FRAME_DTMF_END ? "END" : "BEGIN",
+			rtp->resp, rtp->resp,
+			ast_sockaddr_stringify(&remote_address));
 		rtp->f.frametype = type;
 		rtp->f.subclass.integer = rtp->resp;
 	}