esp_netif_init() returns standard esp_err_t error code (unlike tcpip_adapter init), so shall be checked for the return value
Also to make the initialization code more consistent.
The MQTT broker URL used as default in the examples has ceased operation. All examples and documention have been updated to point to the new domain mqtt.eclipse.org.
This also required an update of the python example test scripts to use TLS 1.2
testing conditions:
transports (tcp, ssl, ws..)
qos (0, 1, 2)
short repeated messages (packed packets)
oversized messages (fragmented packets)
publish from a different thread
Closes https://github.com/espressif/esp-idf/issues/2870 by means of including commit 815623dfe5a0e41fa0e51ab4e336feb3eaa5ba15 from esp-mqtt
Closes https://github.com/espressif/esp-idf/issues/2975 by means of including commit 752953dc3be007cca4255b66a35d3087e61f6a54 from esp-mqtt
Closes https://github.com/espressif/esp-idf/issues/2850 by means of including commits df455d2a5fe562dd1b8351da99a1d6d82b66eff3 17fd713bced4f2d00df7ed664ed82a7d108ab317 from esp-mqtt
