Improved the stubs for event queue and nsapi_dns, to allow checking if callback are handled correctly. This involves some memory allocation and deallocation.
The NetworkStackWrapper is not covered as it seems to be deprecated code.
Most functions are empty or simply return "UNSUPPORTED", but it is still worth covering this functions with unit tests to have better control of unwanted changes.
Added more tests, improved the existing ones. setblocking tests were not checking anything, so they were removed and these functions are called in TCPSocket tests instead.
Add functional and line coverage for UDPSocket and TCPSocket. The EventFlagsstub and NetworkStackstub classes are allowed to store multiple return values to allow running internal loops multiple times.