For issue #223

[vinhlq]

• In the sendPacket() function, when timer is expired mqttwrite() function is not excute. So to give it a change to send ack packet (issue Suspected bug with MQTTYield() / cycle() #223), we need to define a minimal timeout
• The send packet timeout is defined by MIN_SEND_PACKET_TIMEOUT_MS macro

[xw0323]

It is a bug. Please refer to 287 line of https://github.com/evrythng/evrythng-c-library/blob/master/embedded-mqtt/MQTTClient-C/src/MQTTClient.c, and change platform_timer_countdown(&t, c->command_timeout_ms); to TimerCountdownMS(timer, c->command_timeout_ms);

[icraggs]

We're starting to look at this project after a long interval. I intend to resolve this by taking the same approach as in the C++ client code, which is to attempt the packet send at least once. So I'll close this PR, but thank you.