loader: Add benchmark for noop ELF write
loader: Add benchmark for noop ELF write

Add baseline benchmark for writing an existing elf to a new location.

Example run:

    $ sudo make bench-privileged TESTPKGS=pkg/datapath/loader BENCH=CompileOrLoad
    pkg: github.com/cilium/cilium/pkg/datapath/loader
    BenchmarkCompileOrLoad-4             200          10715695 ns/op
    PASS
    ok      github.com/cilium/cilium/pkg/datapath/loader    3.494s

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

michi-covalent/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,cilium-team/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium