Currently we fill as much as posible data in a socket and then use
half of these data to make a flow in the connection.

These data is send and recv buffers. When a connection is dumped and
restored, it needs time to go back to the normal work. In this time we
can reliably fill only send buffers. So at the result the sockets may
contain less data than required for heartbeating and the test will
block.

The test with this patch will monitor actuall size of data in a test
socket.

Cc: Konstantin Neumoin <kneumoin@parallels.com>
Reported-by: Konstantin Neumoin <kneumoin@parallels.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>