The intention was to make sure, that only one packet is sent at a time.
And thus read has to return exactly the size of one packet.

But it doesnt' work as expected, because size of autofs_v5_packet_union
differs on 32 bit and 64 bit architectures.

This is a bug, but it's hidden so deeply, that no one really cares by the
following 2 aspects:

 1) Autofs pipe has O_DIRECT flag, which means excess bytes will be discarded
    upon read.
 2) No one tries to read more than one packet size at a time.

So let's fix the test instead and do not try to read more bytes, than
expected.
Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>