bpf: Move cgroup iterator helpers to bpf.h

Upstream commit: 9621e60f59eae87eb9ffe88d90f24f391a1ef0f0

Move them into bpf.h given we also need them in core code.

BUG=b/438183726
TEST=presubmit
RELEASE_NOTE=None

cos-patch: security-high
Change-Id: I66a800691b7843925197249a2ecbbb9984691641
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/109214
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>
2 files changed