Compatible with EMQX broker

[alvin1221]

Hi there, We have tested that wolfMQTT client connect to emqx broker successfully, also publish & subscribe message are working fine. I hope EMQX broker can be added to the broker compatibility list of README.md, thanks !

MQTT v3.1.1

./examples/mqttclient/mqttclient -h "broker.emqx.io" 
MQTT Client: QoS 0, Use TLS 0
MQTT Net Init: Success (0)
MQTT Init: Success (0)
NetConnect: Host broker.emqx.io, Port 1883, Timeout 5000 ms, Use TLS 0
MQTT Socket Connect: Success (0)
MQTT Connect: Proto (v3.1.1), Success (0)
MQTT Connect Ack: Return Code 0, Session Present 0
MQTT Subscribe: Success (0)
  Topic wolfMQTT/example/testTopic, Qos 0, Return Code 0
MQTT Publish: Topic wolfMQTT/example/testTopic, Success (0)
MQTT Waiting for message...
MQTT Message: Topic wolfMQTT/example/testTopic, Qos 0, Len 4
Payload (0 - 4): test
MQTT Message: Done

MQTT v5

./examples/mqttclient/mqttclient -h "broker.emqx.io"
MQTT Client: QoS 0, Use TLS 0
MQTT Net Init: Success (0)
MQTT Init: Success (0)
NetConnect: Host broker.emqx.io, Port 1883, Timeout 5000 ms, Use TLS 0
MQTT Socket Connect: Success (0)
MQTT Connect: Proto (v5), Success (0)
MQTT Connect Ack: Return Code 0, Session Present 0
MQTT Connect Ack: Assigned Client ID: WolfMQTTClient
MQTT Subscribe: Success (0)
  Topic wolfMQTT/example/testTopic, Qos 0, Return Code 0
MQTT Publish: Topic wolfMQTT/example/testTopic, Success (0)
MQTT Waiting for message...
MQTT Message: Topic wolfMQTT/example/testTopic, Qos 0, Len 4
Payload (0 - 4): test
MQTT Message: Done

[embhorn]

Perfect, thank you @alvin1221 !

[embhorn]

Added to readme. Fixed by #297