quic: measure GRO performance and enable it via config

UDP GRO is supposed to improve socket read performance on client side but currently our code performs very poorly in nighthawk client, by reading one packet per read while allocating 24k buffer. It will be worthwhile to invest the suitable traffic patten for GRO.
Meanwhile this feature is disabled in https://github.com/envoyproxy/envoy/pull/19088 and it will be good to exposed it via a config knob after we know the suitable use case.

And there was a bug reported that the socket reading code allocating 24k buffer per read might lead to MSG_TRUNC and cause packets dropped occasionally. We should change the value to be 64k which is the max GRO receive buffer allowed by the kernel.