Connect to a PF_UNIX server listening on the given path.

async def unixconnect(path):
    '''
    Connect to a PF_UNIX server listening on the given path.
    '''
    reader, writer = await asyncio.open_unix_connection(path=path)
    info = {'path': path, 'unix': True}
    return await Link.anit(reader, writer, info=info)