ethernet: use TrackRecord backtrace for better failure logs

Test: atest EthernetManagerTest
Change-Id: Ifcc038281164b0d840bfc52524e7ac4d32c640a0
diff --git a/tests/cts/net/src/android/net/cts/EthernetManagerTest.kt b/tests/cts/net/src/android/net/cts/EthernetManagerTest.kt
index 11203d7..76a955b 100644
--- a/tests/cts/net/src/android/net/cts/EthernetManagerTest.kt
+++ b/tests/cts/net/src/android/net/cts/EthernetManagerTest.kt
@@ -277,7 +277,7 @@
 
         fun eventuallyExpect(expected: CallbackEntry) {
             val cb = events.poll(TIMEOUT_MS) { it == expected }
-            assertNotNull(cb, "Never received expected $expected")
+            assertNotNull(cb, "Never received expected $expected. Received: ${events.backtrace()}")
         }
 
         fun eventuallyExpect(iface: EthernetTestInterface, state: Int, role: Int) {