net: apps: test_15_4 fixes when running in one qemu

Made the test_15_4 application to run much faster when it is
running inside qemu (started with make qemu0).

Change-Id: I4455eca4f0426e8acc8b87d93eb80f4d179a1b48
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>