Fix comment on bandwidth sampler.

Summary:
The comment is the reverse of the actual logic.  When app-limited, bandwidth samples are not considered valid, because the data being sent is being limited by the application and not the network.

Created from CodeHub with https://fburl.com/edit-in-codehub

Reviewed By: jbeshay

Differential Revision: D65976022

fbshipit-source-id: 0c52bab2edb560afe5e885b0df33090935490778

quic/congestion_control/BbrBandwidthSampler.cpp

@@ -125,7 +125,7 @@ void BbrBandwidthSampler::onPacketAcked(
     }
     Bandwidth measuredBandwidth = sendRate > ackRate ? sendRate : ackRate;
 
-    // This is a valid sample if the packet was sent while app-limited or
+    // This is a valid sample if the packet was sent while not app-limited or
     // it's higher than the current sample.
     if (!ackedPacket.isAppLimited || measuredBandwidth > latestSample_) {
       latestSample_ = measuredBandwidth;