Initialize and destroy mutexes and conditions to be consistent with the rest of the codebase

[Frenzie]

• suspend_cond_mutex the same as every other mutex in janus_audiobridge.c (and elsewhere)
• suspend_cond the same as in src/transports/janus_mqtt.c

janus-gateway/src/transports/janus_mqtt.c

Lines 564 to 565 in fcfd0c5

	janus_mutex_init(&ctx->disconnect.mutex);
	janus_condition_init(&ctx->disconnect.cond);

janus-gateway/src/transports/janus_mqtt.c

Lines 1682 to 1683 in fcfd0c5

	janus_mutex_destroy(&ctx->disconnect.mutex);
	janus_condition_destroy(&ctx->disconnect.cond);

[januscla]

Thanks for your contribution, @Frenzie! Please make sure you sign our CLA, as it's a required step before we can merge this.