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 <sgarzare@redhat.com>

Author: stefano-garzarella

test/sys/test_socket.rs

@@ -1507,17 +1507,11 @@ pub fn test_vsock() {
                     SockFlag::empty(), None)
              .expect("socket failed");
 
-    // VMADDR_CID_HYPERVISOR and VMADDR_CID_LOCAL are reserved, so we expect
-    // an EADDRNOTAVAIL error.
+    // VMADDR_CID_HYPERVISOR is reserved, so we expect an EADDRNOTAVAIL error.
     let sockaddr = SockAddr::new_vsock(libc::VMADDR_CID_HYPERVISOR, port);
     assert_eq!(bind(s1, &sockaddr).err(),
                Some(Error::Sys(Errno::EADDRNOTAVAIL)));
 
-    let sockaddr = SockAddr::new_vsock(libc::VMADDR_CID_LOCAL, port);
-    assert_eq!(bind(s1, &sockaddr).err(),
-               Some(Error::Sys(Errno::EADDRNOTAVAIL)));
-
-
     let sockaddr = SockAddr::new_vsock(libc::VMADDR_CID_ANY, port);
     assert_eq!(bind(s1, &sockaddr), Ok(()));
     listen(s1, 10).expect("listen failed");