vsock_test: update message bounds test for MSG_EOR

Set 'MSG_EOR' in one of message sent, check that 'MSG_EOR'
is visible in corresponding message at receiver.

Signed-off-by: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210903123321.3273866-1-arseny.krasnov@kaspersky.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>