In order to keep sending keep alive messages in the scenario were client
publish too often with QoS0 the keepalive is updated when the response
is received.
Added a separate config value to allow disable the keepalive mechanism (and keep the existing API the same)
Internally though, the keepalive value (in connect_info) is in line with 3.1.2.10 Keep Alive from mqtt spec:
* keepalive=0: Keep alive mechanism disabled (server not to disconnect the client on its inactivity)
* period in seconds to send a Control packet if inactive
Closes https://github.com/espressif/esp-mqtt/issues/179
Previously, uint32_t and size_t were used interchangeably. These types are
interchangeable on Xtensa gcc (uint32_t == size_t == unsigned int), but not on most
other 32-bit gcc architectures (where uint32_t == unsigned long, size_t ==
unsigned int).
Add config option for selecting protocol version at runtime.
This also fixed MQTT protocol version 3.1 which wasnt working with the original implementation
Closes https://github.com/espressif/esp-idf/issues/4448
Closes IDFGH-2311
Closes IDF-1320
This commit adds an event information "connect_return_code" that is written
when the client state is MQTT_STATE_INIT, and the connection fails.
This event info can then be written by the user app to find out the reason
of the fail connection.
Merges https://github.com/espressif/esp-mqtt/pull/100
