Combine packet_ack Quic trace from one packet into one trace
Combine packet_ack Quic trace from one packet into one trace

Summary:
Now that packet_sent is gone, there is no point for each acked packet
to be traced separately as a packet_ack with packet number logged. So change
this to a packets_acked with acked bytes to reduce tracing cost

Reviewed By: mjoras

Differential Revision: D18913498

fbshipit-source-id: 58ffa85c9d0a30b62206057248a8996fe5a634f5

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