elf: fix libbpf integration tests
elf: fix libbpf integration tests

The integration tests are currently broken. When running them in parallel,
the file variable is captured by the closure in t.Run, and so we only
ever try to load a single file.

Fix this by taking an explicit copy of the filename. This is turn makes the
tests fail, since there is plenty of libbpf stuff that we don't understand.

Related to #92

cilium/ebpf,cilium/ebpf