[core][API] Obtaining local interfaces to allow getting connected device name

[ethouris]

This partially restores the recognition facility as provided in #377 and uses it to obtain the device name.

This introduces an internal function GetLocalInterfaces(), which is in use by applications and for internal purposes, and a new API function, srt_getsockdevname, which extracts the device name of the connected socket. This is also in use by a testing application so that the connected status is displayed in Verbose mode.

Note that it doesn't have a guaranteed working in every case. So far it is tested on:

• Linux: reports the interface name, like e.g. "eth0".
• Windows/Cygwin: reports a string in the form of {UUID}, also if the device being used is VPN.
• Windows/WSL: "lo" is reported correctly, as well as conecting locally to the address of "eth0" shows the name correctly. But it reports nothing, if tested against a peer in VPN. Inside tracking shows that the VPN device is not visible among local addresses. The address obtained through srt_getsockname seems to be the VPN-assigned local name, but it is not present in the results of GetLocalInterfaces().

[ethouris]

Problem: I turned this option on on the C++11/Windows CI workflow and it results in a linker error for this newly introduced function. Strange at least, and likely it needs some Windows linker trick to function.