testutils: use unicast MACs in simple_eth_pkt

This "simple" function shouldn't create multicast packets. Changed to use the
same MACs as the other packet creation functions.

Reported by Tony van der Peet <tony.vanderpeet@gmail.com>.
diff --git a/src/python/oftest/testutils.py b/src/python/oftest/testutils.py
index 6892b39..7a096d9 100644
--- a/src/python/oftest/testutils.py
+++ b/src/python/oftest/testutils.py
@@ -418,8 +418,8 @@
     return pkt
 
 def simple_eth_packet(pktlen=60,
-                      eth_dst='01:80:c2:00:00:00',
-                      eth_src='00:01:02:03:04:05',
+                      eth_dst='00:01:02:03:04:05',
+                      eth_src='00:06:07:08:09:0a',
                       eth_type=0x88cc):
 
     if MINSIZE > pktlen: