nbd/client: refactor TRACE of NBD_MAGIC

We are going to switch from TRACE macro to trace points,
this TRACE complicates things, this patch simplifies it.
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20170707152918.23086-7-vsementsov@virtuozzo.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

nbd/client.c

@@ -461,15 +461,8 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         goto fail;
     }
 
-    TRACE("Magic is %c%c%c%c%c%c%c%c",
-          qemu_isprint(buf[0]) ? buf[0] : '.',
-          qemu_isprint(buf[1]) ? buf[1] : '.',
-          qemu_isprint(buf[2]) ? buf[2] : '.',
-          qemu_isprint(buf[3]) ? buf[3] : '.',
-          qemu_isprint(buf[4]) ? buf[4] : '.',
-          qemu_isprint(buf[5]) ? buf[5] : '.',
-          qemu_isprint(buf[6]) ? buf[6] : '.',
-          qemu_isprint(buf[7]) ? buf[7] : '.');
+    magic = ldq_be_p(buf);
+    TRACE("Magic is 0x%" PRIx64, magic);
 
     if (memcmp(buf, "NBDMAGIC", 8) != 0) {
         error_setg(errp, "Invalid magic received");