Clear all APF memory in testDropPingReply() in preparing stage

Modified testDropPingReply() to clear the entire APF memory instead of
only the first byte.  This addresses a known firmware issue with
handling programs smaller than 8 bytes.

Bug: 339147921
Test: TH
Change-Id: I651dae8c9daac24b195196c03b54e69a757de8a7
diff --git a/tests/cts/net/src/android/net/cts/ApfIntegrationTest.kt b/tests/cts/net/src/android/net/cts/ApfIntegrationTest.kt
index 5662fca..710f0fb 100644
--- a/tests/cts/net/src/android/net/cts/ApfIntegrationTest.kt
+++ b/tests/cts/net/src/android/net/cts/ApfIntegrationTest.kt
@@ -436,12 +436,7 @@
         assumeApfVersionSupportAtLeast(4)
 
         // clear any active APF filter
-        var gen = ApfV4Generator(
-                caps.apfVersionSupported,
-                caps.maximumApfProgramSize,
-                caps.maximumApfProgramSize
-        ).addPass()
-        installProgram(gen.generate())
+        clearApfMemory()
         readProgram() // wait for install completion
 
         // Assert that initial ping does not get filtered.
@@ -455,7 +450,7 @@
         assertThat(packetReader.expectPingReply()).isEqualTo(data)
 
         // Generate an APF program that drops the next ping
-        gen = ApfV4Generator(
+        val gen = ApfV4Generator(
                 caps.apfVersionSupported,
                 caps.maximumApfProgramSize,
                 caps.maximumApfProgramSize