bpf: Consistently use bpf_rcu_lock_held() everywhere

bpf: Consistently use bpf_rcu_lock_held() everywhere

We have many places which open-code what's now is bpf_rcu_lock_held()
macro, so replace all those places with a clean and short macro invocation.
For that, move bpf_rcu_lock_held() macro into include/linux/bpf.h.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20251014201403.4104511-1-andrii@kernel.org