* Start working on fixing doxygen warnings

* Upgrade doxyfile to Doxygen 1.9.1

* Clean up some unmatched groups and add some exclusions

* Fix docs for rtos::ThisThread not showing up

* Fix up KV store docs

* Fix incorrect @files, some more incorrect groups

* Fix lots of broken links

* Start fixing mbedtls groups

* Fix more mbedtls docs

* Fix remaining mbedtls files with missing or incorrect grouping

* Fix a huge amount of PSA docs errors

* Fix a few more mbedtls docs errors

* Fix __cplusplus not defined for docs, clean up call in callback typedef, fix some docs errors

* Fix some broken doc links in HAL headers

* Fix more PSA doc errors

* Fix some doxygen errors in networking code

* Fix lots of network related doc errors

* Try and fix some CI failures

* Use Doxygen Action instead of doxygen in Mbed container to get the right version

* Try removing docs check

* Add first part of doxygen action

* Add next part of doxygen action

* Fix yaml syntax error

* Add in license check fix

* Try using verbose scancode

* Fix some more docs issues, workaround scancode-toolkit#3179

* Clean up the LoRaRadio get_state() function on each implementation.  Also fix some other compile and doc errors.

* Fix all remaining doxygen errors

* Fix escaping, for realsies this time

* Remove Doxygen unsupported config options, fix some more get_status() declarations

* Fix some UNITTESTS build errors

* Fix one more compile error

* Another unittest error

As a default implementation is already provided by
NetworkStack, stub implementations in the child classes
are not required. Furthermore, they return unsupported for
all cases instead of redirecting to the non-control API,
which is plainly wrong.

This patch contains improvements mentioned in the unresolved PR
comments:
- function names were changed from socket_sendmsg/socket_recvmsg to
  socket_sendto_control/socket_recvfrom_control.
- default implementation of this functions was provided in the
  NetworkStack class.
- MsgHeaderIterator accesses elements on the aligned addresses.

-Remove Nanostack::add_ethernet_interface API change
-Add get_mac_address to MeshEthernetInterface
-Fix compiler warnings by adding overrides

Remove unnecessary method: add_ethernet_interface_ns

Add support to set and get MAC address from EMAC interface.

Inherit methods gethostbyname, gethostbyname_async and get_dns_server
to Nanostack class. Methods will try to find DNS server address
or DNS query results from Nanostack DNS cache.

```
connectivity
├── netsocket
├── lwipstack
├── nanostack
│   ├── mbed_lib.json // nanostack-interface's mbed_lib.json
│   ├── include
│   │   └── nanostack // headers from features/netsocket/nanostack-interface
│   ├── source        // sources from features/netsocket/nanostack-interface
│   ├── coap-service  // used by Thread only - deprecate?
│   ├── mbed-mesh-api
│   ├── nanostack-hal-mbed-cmsis-rtos // HAL porting layer for Nanostack on mbed with CMSIS-RTOS
│   ├── sal-stack-nanostack
│   └── sal-stack-nanostack-eventloop
├── cellular                // previously in features/cellular/framework/
├── ...

```

This PR is a part of a wider \connectivity refactoring and implements the above new directory structure for \nanostack.