libbpf-tools: fix arg_num field for positional arguments am: c749a59d33 am: c209d5184c am: f8d3d1d682 am: 5669ac1c10 am: 63a19a4d3b

Original change: https://android-review.googlesource.com/c/platform/external/bcc/+/2052235

Change-Id: Ie53173c538bc81d03e46f1bb7b18089051d3d13e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>