[$] Kernel operations structures in BPF

One of the more eyebrow-raising features to go into the 5.6 kernel is theability to load TCP congestion-control algorithms as BPF programs; networking developer Toke Hiiland-Jirgensen described it as acontinuation of the kernel's "march towards becoming BPFruntime-powered microkernel". On itsface, congestion control is a significant new functionality to hand over toBPF, taking it farbeyond its existing capabilities. When one looks closer, though, one'seyebrow altitude may well increase further; the implementation of thisfeature breaks new ground in a couple of areas.