tests: do not try to read more than packet in AutoFS test

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>

test/zdtm/static/autofs.c

@@ -460,7 +460,7 @@ static int automountd_loop(int pipe, const char *mountpoint, struct autofs_param
 {
 	union autofs_v5_packet_union *packet;
 	ssize_t bytes;
-	size_t psize = sizeof(*packet) + 1;
+	size_t psize = sizeof(*packet);
 	int err = 0;
 
 	packet = malloc(psize);
@@ -473,7 +473,7 @@ static int automountd_loop(int pipe, const char *mountpoint, struct autofs_param
 	siginterrupt(SIGUSR2, 1);
 
 	while (!stop && !err) {
-		memset(packet, 0, sizeof(*packet));
+		memset(packet, 0, psize);
 
 		bytes = read(pipe, packet, psize);
 		if (bytes < 0) {
@@ -483,12 +483,9 @@ static int automountd_loop(int pipe, const char *mountpoint, struct autofs_param
 			}
 			continue;
 		}
-		if (bytes == psize) {
-			pr_err("read more that expected\n");
-			return -EINVAL;
-		}
-		if (bytes != sizeof(*packet)) {
-			pr_err("read less than expected: %zd\n", bytes);
+		if (bytes != psize) {
+			pr_err("read less than expected: %zd < %zd\n",
+					bytes, psize);
 			return -EINVAL;
 		}
 		err = automountd_serve(mountpoint, param, packet);