MacAddress: address api review comments

1) toSafeString() is renamed to toOuiString()
2) toOuiString() returns a String that only contains the first 3 bytes
   of the mac address.

Bug: 70336442
Test: runtest frameworks-net
Change-Id: I798d8fec32dbff5687a682028e5d90eb941f81c1
Merged-In: I798d8fec32dbff5687a682028e5d90eb941f81c1

(cherry pick from commit 3f83b8ad4e50b8ac75cf937bba7ff46c9c6c73c1)
diff --git a/core/java/android/net/MacAddress.java b/core/java/android/net/MacAddress.java
index 3458861..d6992aa 100644
--- a/core/java/android/net/MacAddress.java
+++ b/core/java/android/net/MacAddress.java
@@ -130,11 +130,12 @@
     }
 
     /**
-     * @return a String representation of the OUI part of this MacAddres,
-     * with the lower 3 bytes constituting the NIC part replaced with 0.
+     * @return a String representation of the OUI part of this MacAddress made of 3 hexadecimal
+     * numbers in [0,ff] joined by ':' characters.
      */
-    public String toSafeString() {
-        return stringAddrFromLongAddr(mAddr & OUI_MASK);
+    public String toOuiString() {
+        return String.format(
+                "%02x:%02x:%02x", (mAddr >> 40) & 0xff, (mAddr >> 32) & 0xff, (mAddr >> 24) & 0xff);
     }
 
     @Override
diff --git a/tests/net/java/android/net/MacAddressTest.java b/tests/net/java/android/net/MacAddressTest.java
index 558dbb6..473dc53 100644
--- a/tests/net/java/android/net/MacAddressTest.java
+++ b/tests/net/java/android/net/MacAddressTest.java
@@ -73,18 +73,18 @@
     }
 
     @Test
-    public void testToSafeString() {
+    public void testToOuiString() {
         String[][] macs = {
-            {"07:00:d3:56:8a:c4", "07:00:d3:00:00:00"},
-            {"33:33:aa:bb:cc:dd", "33:33:aa:00:00:00"},
-            {"06:00:00:00:00:00", "06:00:00:00:00:00"},
-            {"07:00:d3:56:8a:c4", "07:00:d3:00:00:00"}
+            {"07:00:d3:56:8a:c4", "07:00:d3"},
+            {"33:33:aa:bb:cc:dd", "33:33:aa"},
+            {"06:00:00:00:00:00", "06:00:00"},
+            {"07:00:d3:56:8a:c4", "07:00:d3"}
         };
 
         for (String[] pair : macs) {
             String mac = pair[0];
             String expected = pair[1];
-            assertEquals(expected, MacAddress.fromString(mac).toSafeString());
+            assertEquals(expected, MacAddress.fromString(mac).toOuiString());
         }
     }