net: tests: Fix the default MAC address

Use the proper MAC address space (00-00-5E-00-53-xx) dedicated
for documentation and specified in RFC 7042 ch 2.1.2.

Change-Id: If8ef9e4ee4e041ad005060664ebafe60df0a6bf9
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>