[$] BBR congestion control

Congestion-control algorithms are unglamorous bits of code that allownetwork protocols (usually TCP) to maximize the throughput of any givenconnection while simultaneously sharing the available bandwidth equitablywith other users. New algorithms tend not to generate a great deal ofexcitement; the addition of TCPNew Vegas during the 4.8 merge window drew little fanfare, for example.The BBR (Bottleneck Bandwidth and RTT)algorithm just released by Google, though, is attracting rather moreattention; it moves away from the mechanisms traditionally used by thesealgorithms in an attempt to get better results in a network characterized bywireless links, meddling middleboxes, and bufferbloat.