selftests: bpf: add missing executables to .gitignore

commit 435f90a3

 ("selftests/bpf: add a test case for sock_ops
perf-event notification") missed adding new test to gitignore.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>