catchunks: Implement CUBIC window adaptation

Also increase the RTT estimator multiplier k to 8.

Change-Id: I68c5096ac0da854f071bab5f7519b1c144f20ca1
refs: #4861
diff --git a/tools/chunks/catchunks/rtt-estimator.hpp b/tools/chunks/catchunks/rtt-estimator.hpp
index 6f10326..47f2ac8 100644
--- a/tools/chunks/catchunks/rtt-estimator.hpp
+++ b/tools/chunks/catchunks/rtt-estimator.hpp
@@ -57,7 +57,7 @@
       : isVerbose(false)
       , alpha(0.125)
       , beta(0.25)
-      , k(4)
+      , k(8)
       , initialRto(1000.0)
       , minRto(200.0)
       , maxRto(20000.0)