selftests: bpf: add missing NET_SCHED to config

CONFIG_NET_SCHED wasn't enabled in arm64's defconfig only for x86.

So bpf/test_tunnel.sh tests fails with:

  RTNETLINK answers: Operation not supported
  RTNETLINK answers: Operation not supported
  We have an error talking to the kernel, -1

Enable NET_SCHED and more tests pass.

Fixes: 3bce593a

 ("selftests: bpf: config: add config fragments")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>