initial commit for VSOCK sockets

[olk]

This commit introduces support for VSOCK sockets on Linux.

TODO:

• documentation
• support for Windows (address family AF_HYPERV, protocol HV_PROTOCOL_RAW)

Note:

• SOCK_DGRAM currently not fully implemented in Linux kernel 6.2.1

[lyuxiaosu]

Hi olk, thanks for the submission. It seems it doesn't support async_connect(), is it possible to support it? Thanks very much.