change MAC address hash to reduce collisions

Change-Id: I0ec7b53edcfce27508b0ea862da63597aa0ad3fd
diff --git a/utils/misc/src/main/java/org/onlab/packet/MacAddress.java b/utils/misc/src/main/java/org/onlab/packet/MacAddress.java
index 5c59d22..e9b9113 100644
--- a/utils/misc/src/main/java/org/onlab/packet/MacAddress.java
+++ b/utils/misc/src/main/java/org/onlab/packet/MacAddress.java
@@ -188,7 +188,7 @@
 
     @Override
     public int hashCode() {
-        return Arrays.hashCode(this.address);
+        return Long.hashCode(toLong());
     }
 
     @Override