Fixes gcc 8.3.1 build failure due to FilterChainBenchmarkFixture::Set…

…Up hiding base-class virtual functions (#8071)

Description: I'm seeing "bazel-out/k8-fastbuild/bin/external/com_github_google_benchmark/_virtual_includes/benchmark/benchmark/benchmark.h:1071:16: error: 'virtual void benchmark::Fixture::SetUp(benchmark::State&)' was hidden" when running tests. This resolves the issue with hiding of the base-class functions.
Risk Level: low
Testing:
Docs Changes:
Release Notes:

Signed-off-by: Dmitri Dolguikh <ddolguik@redhat.com>

test/server/filter_chain_benchmark_test.cc

@@ -149,6 +149,7 @@ const char YamlSingleDstPortBottom[] = R"EOF(
 
 class FilterChainBenchmarkFixture : public benchmark::Fixture {
 public:
+  using Fixture::SetUp;
   void SetUp(const ::benchmark::State& state) override {
     int64_t input_size = state.range(0);
     std::vector<std::string> port_chains;