ethernet: test adding listener after removing server mode iface

Tests that registering a EthernetStateListener functions as expected
after requesting a tethering interface and subsequently removing that
interface.

Test: atest testCallbacks_afterRemovingServerModeInterface
Bug: 290971780
Change-Id: I7b6e1a3b3ac23f4fbdd2d20f63f83d59c4d4999d

tests/cts/net/src/android/net/cts/EthernetManagerTest.kt

@@ -667,6 +667,20 @@ class EthernetManagerTest {
         listener.expectCallback(iface, STATE_LINK_UP, ROLE_CLIENT)
     }
 
+    @Test
+    fun testCallbacks_afterRemovingServerModeInterface() {
+        // do not run this test if an interface that can be used for tethering already exists.
+        assumeNoInterfaceForTetheringAvailable()
+
+        val iface = createInterface()
+        requestTetheredInterface().expectOnAvailable()
+        removeInterface(iface)
+
+        val listener = EthernetStateListener()
+        addInterfaceStateListener(listener)
+        listener.assertNoCallback()
+    }
+
     @Test
     fun testGetInterfaceList() {
         // Create two test interfaces and check the return list contains the interface names.