Logging in series of examples has misuse of "%d" instead of type-appropriate format specifiers.
Fix by changing "%d" to PRIxx macros corresponding to type.
Remove -Wno-format compile flag in those examples that are affected.
- Removes extra callback function, the code from the callback is integrated into the event handler code.
- Clarify usage of handler args, pass NULL as callback data instead of client, to avoid user confusion,
and add documentation on usage of handler_args.
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.
