vsock: reset socket state when de-assigning the transport

Transport's release() and destruct() are called when de-assigning the
vsock transport. These callbacks can touch some socket state like
sock flags, sk_state, and peer_shutdown.

Since we are reassigning the socket to a new transport during
vsock_connect(), let's reset these fields to have a clean state with
the new transport.

Fixes: c0cfa2d8 ("vsock: add multi-transports support")
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>