gh-119461: Fix ThreadedVSOCKSocketStreamTest (#119465)

Add socket.VMADDR_CID_LOCAL constant.

Fix ThreadedVSOCKSocketStreamTest: if get_cid() returns the host
address or the "any" address, use the local communication address
(loopback): VMADDR_CID_LOCAL.

On Linux 6.9, apparently, the /dev/vsock device is now available but
get_cid() returns VMADDR_CID_ANY (-1).