bridge_builtin_features.c: Set auto(mix)mon variables on both channels

This is how features behaved up through Asterisk 11, but was changed
when the new bridging framework was implemented in Asterisk 12.

Reported by rrittgarn in #asterisk.

Change-Id: I72cf86223947a8118c75f46e2c603dbc11e3125b

CHANGES

@@ -71,6 +71,19 @@ Bridging
    ast_bridge_snapshot_update structure as it's data.  It contains
    the last snapshot and the new one.
 
+Features
+------------------
+ * Before Asterisk 12, when using the automon or automixmon features defined
+   in features.conf, a channel variable (TOUCH_MIXMONITOR_OUTPUT) was set on
+   both channels, indicating the filename of the recording.
+
+   When bridging was overhauled in Asterisk 12, the behavior was changed such
+   that the variable was only set on the peer channel and not on the channel
+   that initiated the automon or automixmon.
+
+   The previous behavior has been restored so both channels receive the
+   channel variable when one of these features is invoked.
+
 ------------------------------------------------------------------------------
 --- Functionality changes from Asterisk 16.0.0 to Asterisk 16.1.0 ------------
 ------------------------------------------------------------------------------

bridges/bridge_builtin_features.c

@@ -213,6 +213,7 @@ static void start_automonitor(struct ast_bridge_channel *bridge_channel, struct
 		ast_bridge_channel_write_playfile(bridge_channel, NULL, start_message, NULL);
 	}
 
+	pbx_builtin_setvar_helper(bridge_channel->chan, "TOUCH_MONITOR_OUTPUT", touch_filename);
 	pbx_builtin_setvar_helper(peer_chan, "TOUCH_MONITOR_OUTPUT", touch_filename);
 }
 
@@ -400,6 +401,7 @@ static void start_automixmonitor(struct ast_bridge_channel *bridge_channel, stru
 		ast_bridge_channel_write_playfile(bridge_channel, NULL, start_message, NULL);
 	}
 
+	pbx_builtin_setvar_helper(bridge_channel->chan, "TOUCH_MIXMONITOR_OUTPUT", touch_filename);
 	pbx_builtin_setvar_helper(peer_chan, "TOUCH_MIXMONITOR_OUTPUT", touch_filename);
 }