Limit sending by the anti-amplification factor

Fixes #3639

draft-ietf-quic-recovery.md

@@ -752,6 +752,12 @@ twice the maximum datagram size. This follows the analysis and recommendations
 in {{?RFC6928}}, increasing the byte limit to account for the smaller 8 byte
 overhead of UDP compared to the 20 byte overhead for TCP.
 
+Prior to validating the client's address, the server can also be limited by
+the anti-amplification limit as specified in Section 8.1 of {{QUIC-TRANSPORT}}.
+Though the anti-amplification limit can prevent the congestion window from
+being fully utilized and therefore slow down the increase in congestion window,
+it does not directly affect the congestion window.
+
 The minimum congestion window is the smallest value the congestion window can
 decrease to as a response to loss, ECN-CE, or persistent congestion.
 The RECOMMENDED value is 2 * max_datagram_size.