Add __NR_bpf constant for i686.

This adds support for running the net tests on 32-bit x86.

Bug: 79532682
Bug: 117749037

Test: run vts -m VtsKernelNetTest
Test result after change: PASSED: 2, FAILED: 0, MODULES: 2 of 2


Signed-off-by: Alistair Strachan <astrachan@google.com>
Change-Id: I5a8ade3a2292734001dd6e85f9c6b5cefc8de9c1
Merged-in: I5a8ade3a2292734001dd6e85f9c6b5cefc8de9c1
(cherry picked from commit 7993a855)