Fix test_vsock failure on VMADDR_CID_LOCAL testing
Fix test_vsock failure on VMADDR_CID_LOCAL testing

Starting from Linux 5.6, VMADDR_CID_LOCAL is supported to do local
communication (loopback device).

Before Linux 5.6 it was called VMADDR_CID_RESERVED and was not
supported, so we could expect an EADDRNOTAVAIL, but now this address
is supported and handled by the 'vsock_loopback' kernel module loaded
automatically if no other vsock transports are loaded.

Issue #1310
Issue #1403

Signed-off-by: Stefano Garzarella <6f3dd2004310421c0dda1107f4857e62a774d5df@redhat.com>

geofft/nix-rust,nix-rust/nix,geofft/nix-rust,geofft/nix-rust,asomers/nix,asomers/nix,nix-rust/nix