bridge_basic: Change warning to verbose if transfer cancelled

The attended transfer feature will emit a warning if the user
cancels the transfer or the attended transfer doesn't complete
for any reason. Changes the warning to a verbose message,
since nothing is actually wrong here.

ASTERISK-29612 #close

Change-Id: I64c93cdb21360a0a8d45e9cb6db3af8168f66e6d

main/bridge_basic.c

@@ -3352,13 +3352,12 @@ static int feature_attended_transfer(struct ast_bridge_channel *bridge_channel,
 	/* Grab the extension to transfer to */
 	if (grab_transfer(bridge_channel->chan, exten, sizeof(exten), props->context)) {
 		/*
-		 * XXX The warning here really should be removed.  While the
-		 * message is accurate, this is a normal exit for when the user
-		 * fails to specify a valid transfer target.  e.g., The user
+		 * This is a normal exit for when the user fails
+		 * to specify a valid transfer target.  e.g., The user
 		 * hungup, didn't dial any digits, or dialed an invalid
 		 * extension.
 		 */
-		ast_log(LOG_WARNING, "Channel %s: Unable to acquire target extension for attended transfer.\n",
+		ast_verb(3, "Channel %s: Unable to acquire target extension for attended transfer.\n",
 			ast_channel_name(bridge_channel->chan));
 		ast_bridge_channel_write_unhold(bridge_channel);
 		attended_transfer_properties_shutdown(props);