Add TLS ALPN option to be set when connecting MQTT

This is required to be set to "mqtt" for instance when connecting
to the AWS IoT Core data endpoint at port 443 to indicate we're
sending MQTT, because in that case websocket and mqtt shares the same
port for whatever reason.

daemon/main.c

@@ -559,6 +559,7 @@ static void options(int *argc, char ***argv) {
 #ifdef HAVE_MQTT
 		{ "mqtt-host",0,0,	G_OPTION_ARG_STRING,	&rtpe_config.mqtt_host,	"Mosquitto broker host or address",	"HOST|IP"},
 		{ "mqtt-port",0,0,	G_OPTION_ARG_INT,	&rtpe_config.mqtt_port,	"Mosquitto broker port number",		"INT"},
+		{ "mqtt-tls-alpn",0,0,	G_OPTION_ARG_STRING,	&rtpe_config.mqtt_tls_alpn,	"Mosquitto broker TLS ALPN",	"STRING"},
 		{ "mqtt-id",0,0,	G_OPTION_ARG_STRING,	&rtpe_config.mqtt_id,	"Mosquitto client ID",			"STRING"},
 		{ "mqtt-keepalive",0,0,	G_OPTION_ARG_INT,	&rtpe_config.mqtt_keepalive,"Seconds between mosquitto keepalives","INT"},
 		{ "mqtt-user",0,0,	G_OPTION_ARG_STRING,	&rtpe_config.mqtt_user,	"Username for mosquitto auth",		"USERNAME"},

daemon/mqtt.c

@@ -61,6 +61,14 @@ static int mqtt_connect(void) {
 		}
 	}
 
+    if (rtpe_config.mqtt_tls_alpn) {
+		int ret = mosquitto_string_option(mosq, MOSQ_OPT_TLS_ALPN, rtpe_config.mqtt_tls_alpn);
+		if (ret != MOSQ_ERR_SUCCESS) {
+			ilog(LOG_ERR, "Failed to set mosquitto TLS ALPN options: %s", mosquitto_strerror(errno));
+			return -1;
+		}
+    }
+
 	ret = mosquitto_connect(mosq, rtpe_config.mqtt_host, rtpe_config.mqtt_port,
 			rtpe_config.mqtt_keepalive);
 	if (ret != MOSQ_ERR_SUCCESS) {

etc/rtpengine.conf

@@ -118,6 +118,7 @@ recording-method = proc
 
 # mqtt-host = localhost
 # mqtt-port = 1883
+# mqtt-tls-alpn = mqtt
 # mqtt-id =
 # mqtt-user = foo
 # mqtt-pass = bar

include/main.h

@@ -135,6 +135,7 @@ struct rtpengine_config {
 	int			poller_per_thread;
 	char			*mqtt_host;
 	int			mqtt_port;
+	char			*mqtt_tls_alpn;
 	char			*mqtt_id;
 	int			mqtt_keepalive;
 	char			*mqtt_user;