Include bpf program in APEXes

bpf program is put to an APEX via 'bpfs' property. It is
placed under etc/bpf directory in it.

Fix: 167530625
Test: m

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/1418308

Merged-In: Ia36b486f0cffb619ecc4f7a318cde881abc5baf4
Change-Id: I42631beea4e668d86ba437d3e2edb392137706f0
(cherry picked from commit 05e47c0c)