Add getRtmFamily for RtNetlinkRouteMessage

Test: atest NetworkStaticLibTests:com.android.net.moduletests.util.netlink.RtNetlinkRouteMessageTest
Change-Id: Ifdf5afc4f58ff55bd20cc60e23b17c3138754392

staticlibs/device/com/android/net/module/util/netlink/RtNetlinkRouteMessage.java

@@ -98,6 +98,13 @@ public class RtNetlinkRouteMessage extends NetlinkMessage {
         mSinceLastUseMillis = -1;
     }
 
+    /**
+     * Returns the rtnetlink family.
+     */
+    public short getRtmFamily() {
+        return mRtmsg.family;
+    }
+
     /**
      * Returns if the route is resolved. This is always true for unicast,
      * and may be false only for multicast routes.

staticlibs/tests/unit/src/com/android/net/module/util/netlink/RtNetlinkRouteMessageTest.java

@@ -16,7 +16,9 @@
 
 package com.android.net.module.util.netlink;
 
+import static android.system.OsConstants.AF_INET6;
 import static android.system.OsConstants.NETLINK_ROUTE;
+import static com.android.net.module.util.netlink.NetlinkConstants.RTNL_FAMILY_IP6MR;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
@@ -342,4 +344,24 @@ public class RtNetlinkRouteMessageTest {
                 + "}";
         assertEquals(expected, routeMsg.toString());
     }
+
+    @Test
+    public void testGetRtmFamily_RTNL_FAMILY_IP6MR() {
+        final ByteBuffer byteBuffer = toByteBuffer(RTM_NEWROUTE_MULTICAST_IPV6_HEX);
+        byteBuffer.order(ByteOrder.LITTLE_ENDIAN);  // For testing.
+        final NetlinkMessage msg = NetlinkMessage.parse(byteBuffer, NETLINK_ROUTE);
+        final RtNetlinkRouteMessage routeMsg = (RtNetlinkRouteMessage) msg;
+
+        assertEquals(RTNL_FAMILY_IP6MR, routeMsg.getRtmFamily());
+    }
+
+    @Test
+    public void testGetRtmFamily_AF_INET6() {
+        final ByteBuffer byteBuffer = toByteBuffer(RTM_NEWROUTE_HEX);
+        byteBuffer.order(ByteOrder.LITTLE_ENDIAN);  // For testing.
+        final NetlinkMessage msg = NetlinkMessage.parse(byteBuffer, NETLINK_ROUTE);
+        final RtNetlinkRouteMessage routeMsg = (RtNetlinkRouteMessage) msg;
+
+        assertEquals(AF_INET6, routeMsg.getRtmFamily());
+    }
 }