Move intf_nbr_tables in AgentNeighborTests to cmdlineoverrides

Summary:
Move interface neighbor tables command line flag in AgentNeighborTests
to the cmdlineoverrides() function.

This was being set in setup() but overridden when the superclass
cmdlineoverrides() was called.

Reviewed By: daiwei1983

Differential Revision: D69198222

fbshipit-source-id: 935c0d8f2901d21c82519cd9459c400b5a32a47d

fboss/agent/test/agent_hw_tests/AgentNeighborTests.cpp

@@ -117,9 +117,9 @@ class AgentNeighborTest : public AgentHwTest {
       NdpTable>;
 
  protected:
-  void SetUp() override {
+  void setCmdLineFlagOverrides() const override {
     FLAGS_intf_nbr_tables = isIntfNbrTable;
-    AgentHwTest::SetUp();
+    AgentHwTest::setCmdLineFlagOverrides();
   }
 
   std::vector<production_features::ProductionFeature>