move l4 source port random to test with truncation

Summary:
As titled, move l4 source port random to test with truncation. This is supported only on J3 and J3 only supports truncation.

This is towards enabling sflow tests on all platforms

Reviewed By: nivinl

Differential Revision: D68535244

fbshipit-source-id: 299ad7e6ca1f2ffdce8fb04cc985203aaf7667be

fboss/agent/test/agent_hw_tests/AgentSflowMirrorTest.cpp

@@ -900,7 +900,7 @@ TEST_F(AgentSflowMirrorTestV6, MoveToV4) {
       setup, verify, setupPostWb, [=, this]() { verifySampledPacket(true); });
 }
 
-TEST_F(AgentSflowMirrorTestV6, verifyL4SrcPortRandomization) {
+TEST_F(AgentSflowMirrorTruncateTestV6, verifyL4SrcPortRandomization) {
   auto setup = [=, this]() {
     auto config = initialConfig(*getAgentEnsemble());
     configureMirror(config, false, 0);