Add a VpnManager.TYPE_VPN_OEM.

This needed for OEMs that have VPN types not supported by AOSP.

Bug: 171872481
Test: new test coverage in VpnTransportInfoTest
Change-Id: Ic7529bef7f12d2c74a3be5b1a4a2d54fb0d0bfac

tests/net/java/android/net/VpnTransportInfoTest.java

@@ -42,7 +42,13 @@ public class VpnTransportInfoTest {
         VpnTransportInfo v1 = new VpnTransportInfo(VpnManager.TYPE_VPN_PLATFORM);
         VpnTransportInfo v2 = new VpnTransportInfo(VpnManager.TYPE_VPN_SERVICE);
         VpnTransportInfo v3 = new VpnTransportInfo(VpnManager.TYPE_VPN_PLATFORM);
+        VpnTransportInfo v4 = new VpnTransportInfo(VpnManager.TYPE_VPN_LEGACY);
+        VpnTransportInfo v5 = new VpnTransportInfo(VpnManager.TYPE_VPN_OEM);
+
         assertNotEquals(v1, v2);
+        assertNotEquals(v3, v4);
+        assertNotEquals(v4, v5);
+
         assertEquals(v1, v3);
         assertEquals(v1.hashCode(), v3.hashCode());
     }