Current lwip implementation does not support deleting a task which is
actively waiting on `select()` or `poll()` API.
Therefore we have to make sure that `select()` exits to deallocate its internal
callback before deleting the task. This is achieved by a shutdown
semaphore which informs the client once the `select()` exitted.
fix slave
add multi register area descriptors into concrete port (initial)
add create/destroy of area descriptors into concrete port
add the list of descriptors in common slave interface structure and init/destroy in concrete slave port
move r/w callback functions into common slave
final update of common slave interface wrappers add override API option in concrete port
update slave examples to check new feature
Add TCP port files to provide Modbus TCP interface for communication
Add freemodbus add tcp support for common master/slave iface and tcp example based on socket API
The communication between master and slave checked for each example serial_master, serial_slave (use ModbusPoll TCP)
update tcp example according netif changes, fix ci issues
update TCP slave implementation
update example_test.py to to set IP through stdin
update API documentation
event bit instead of semahore to lock communication resource
update default options and master/slave port files
Closes https://github.com/espressif/esp-idf/issues/858
Closes IDF-452
yuanjm