bpf: Do not walk twice the hash map on free

If someone stores both a timer and a workqueue in a hash map, on free, we
would walk it twice.

Add a check in htab_free_malloced_timers_or_wq and free the timers and
workqueues if they are present.

Fixes: 246331e3 ("bpf: allow struct bpf_wq to be embedded in arraymaps and hashmaps")
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20240430-bpf-next-v3-2-27afe7f3b17c@kernel.org