Invoke tcpdump with -l

Currently ConnectivityDiagnosticsCollector invokes tcpdump with -U,
which would causes the collector failed to log ending packets due to
packet buffering.

Test:
android.net.cts.TrafficStatsTest#testTrafficStatsForLocalhost
Bug: 393471251
Change-Id: Ibe2977097bdeeef9546ce9c83b1dfd695c31f6d1
diff --git a/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt b/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
index 4b9429b..8a255c6 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
@@ -224,7 +224,7 @@
             // Echo the current pid, and replace it (with exec) with the tcpdump process, so the
             // tcpdump pid is known.
             writer.write(
-                "echo $$; exec su 0 tcpdump -n -i any -U -xx".encodeToByteArray()
+                "echo $$; exec su 0 tcpdump -n -i any -l -xx".encodeToByteArray()
             )
         }
         val reader = FileReader(stdout.fileDescriptor).buffered()