test: deflake Http2FloodMitigationTest RST_STREAM test (#10527)
test: deflake Http2FloodMitigationTest RST_STREAM test (#10527)

Because of the vagaries of the macOS TCP stack, the RST_STREAM
test seems to routinely manage to limit itself to a few outstanding
RST_STREAM packets and the connection closure is never triggered.
Force the backlog to grow by disabling client reads.

Risk Level: low (test only)
Testing: integration test fixed
Docs Changes: n/a
Release Notes: n/a

Signed-off-by: Stephan Zuercher <12de3568c51b3e8be16eecacef359e62ce51b8cc@gmail.com>
envoyproxy/envoy-wasm,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lyft/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lizan/envoy,envoyproxy/envoy-wasm,lizan/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lizan/envoy,istio/envoy,lizan/envoy,istio/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,istio/envoy,istio/envoy,lyft/envoy,istio/envoy,envoyproxy/envoy,istio/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,lizan/envoy