bpf: Add support to retrieve ref_ctr_offset for uprobe perf link

Adding support to retrieve ref_ctr_offset for uprobe perf link,
which got somehow omitted from the initial uprobe link info changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/bpf/20250509153539.779599-2-jolsa@kernel.org