Add a WARNING in bridge_softmix when a timing module isn't loaded

If bridge_softmix fails to be created because no timing source is present in
Asterisk, this will currently fail gracefully but with (most likely) a generic
error message by whatever module tried to create the softmix bridge. This
patch adds a more explicit warning so you can actually diagnose and fix the
problem.

Review: https://reviewboard.asterisk.org/r/2857/
........

Merged revisions 399353 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@399365 65c4cc65-6c06-0410-ace0-fbb531ad65f3

bridges/bridge_softmix.c

@@ -1044,6 +1044,7 @@ static int softmix_bridge_create(struct ast_bridge *bridge)
 	ast_mutex_init(&softmix_data->lock);
 	softmix_data->timer = ast_timer_open();
 	if (!softmix_data->timer) {
+		ast_log(AST_LOG_WARNING, "Failed to open timer for softmix bridge\n");
 		softmix_bridge_data_destroy(softmix_data);
 		return -1;
 	}