Detect BPF tags for license

[pombredanne]

See https://github.com/projectcalico/calico/blob/4ac717de1f4032ddce7112f74d2becc4062c9c49/felix/bpf-apache/filter.c#L102

We are detecting OK... but we could do even better, like handling these as special tags or as packages:

char ____license[] attribute((section("license"))) = "Apache-2.0";

See also:

• https://ebpf.io/blog/ebpf-licensing-guide/
• https://www.kernel.org/doc/html/latest/bpf/bpf_licensing.html
• https://github.com/nyrahul/ebpf-guide/blob/4359bfba59c72b26843c29d0dda0426832a95782/docs/gpl_license_ebpf.rst