res_stasis: Set a video source mode on Stasis created bridges

When a bridge is created via ARI (through res_stasis), no video source
mode is set by default. As a result, any endpoint sending video media
won't ever see any video reflected back to it.

This patch defaults a bridge to a 'follow the talker' video mode.
Further work can be done to add routes that allow for the video mode to
be controlled through the /bridges resource.

Change-Id: I7e9d530a5d7a97a4524a9ee4e468e1a6b3443866

res/res_stasis.c

@@ -798,6 +798,7 @@ struct ast_bridge *stasis_app_bridge_create(const char *type, const char *name,
 
 	bridge = bridge_stasis_new(capabilities, flags, name, id);
 	if (bridge) {
+		ast_bridge_set_talker_src_video_mode(bridge);
 		if (!ao2_link(app_bridges, bridge)) {
 			ast_bridge_destroy(bridge, 0);
 			bridge = NULL;