Forked from #14982 - that issue was originally about adding both a BPF and an eBPF package to x/net.

After researching eBPF more, the virtual machine is very different and more complex, so it makes sense to track the work for eBPF separately from the relatively simple BPF stuff.

Main documentation for eBPF is at https://www.kernel.org/doc/Documentation/networking/filter.txt , although it's described as a diff from "classic" BPF, which is really not a helpful way to specify a machine.