Add received packets timestamps to AckState

Summary:
Store timestamps/packet numbers of recently received packets in AckState.

 - The maximum number of packets stored is controlled by kMaxReceivedPktsTimestampsStored.
- The packet number of entries in the deque is guarenteed to increase
   monotonically because an entry is only added for a received packet
  if the packet number is greater than the packet number of the last
  element in the deque (e.g., entries are not added for packets that
  arrive out of order relative to previously received packets).

Reviewed By: bschlinker

Differential Revision: D37799023

fbshipit-source-id: 3b6bf2ba8ea15219a87bbdc2724fe23eebe66b70

quic/server/state/ServerStateMachine.cpp

@@ -1318,7 +1318,7 @@ void onServerReadDataFromOpen(
     if (conn.peerAddress != readData.peer) {
       // TODO use new conn id, make sure the other endpoint has new conn id
       if (isNonProbingPacket) {
-        if (packetNum == ackState.largestReceivedPacketNum) {
+        if (packetNum == ackState.largestRecvdPacketNum) {
           ShortHeader* shortHeader = regularPacket.header.asShort();
           bool intentionalMigration = false;
           if (shortHeader &&
@@ -1531,10 +1531,10 @@ void onServerReadDataFromClosed(
 
   // We only need to set the largest received packet number in order to
   // determine whether or not we need to send a new close.
-  auto& largestReceivedPacketNum =
-      getAckState(conn, pnSpace).largestReceivedPacketNum;
-  largestReceivedPacketNum = std::max<PacketNum>(
-      largestReceivedPacketNum.value_or(packetNum), packetNum);
+  auto& largestRecvdPacketNum =
+      getAckState(conn, pnSpace).largestRecvdPacketNum;
+  largestRecvdPacketNum =
+      std::max<PacketNum>(largestRecvdPacketNum.value_or(packetNum), packetNum);
 }
 
 void onServerClose(QuicServerConnectionState& conn) {