NetBpfLoader: create /sys/fs/bpf/loader dir

(instead of in platform bpfloader)

Better to do it earlier so we can use it for
auto/permanently pinned/attached networking programs.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I202e150e6d48e63ba643c1bd2247cefcdebc07a5