import ebpf jit from linux 3.17-rc2
Adapt eBPF JIT to user-space and wire it into bench.lua

* src/bench.lua: Adapt to work with BPF and eBPF.

* src/Makefile: Make eBPF library.

* src/ref/bpfe-jit-kernel/bpf_jit.S: Adapt to be loadable in a PIC
  library.

* src/ref/bpfe-jit-kernel/bpf_jit_comp.c:
* src/ref/bpfe-jit-kernel/core.c: Comment out unneeded things, and shim
  Linux interfaces.
* src/ref/bpfe-jit-kernel/filter.c: Likewise.
  (compile_filter, run_filter): New helpers.

* src/ref/bpfe-jit-kernel/hack.h:
* src/ref/bpfe-jit-kernel/hack.c: Add Linux shim interface.
Rationalize the two Linux JIT shared libraries