[llvm] [BPF] fix print_btf.py test script on bigendian machines (PR #110332)

[via llvm-commits]

eddyz87 wrote:

(for the record, the change was tested locally on a big-endian virtual machine, as described [here](https://docs.kernel.org/bpf/s390.html))

https://github.com/llvm/llvm-project/pull/110332