Support dual-license under bpf

[hzxuzhonghu]

What would you like to be added:

The motivation for this is to be compliant with the CNCF IP policy.

We should select T GPL 2.0 and the 2-Clause BSD: GPL-2.0-only OR BSD-2-Clause. The 2-Clause BSD was selected because:

• It is one of the approved licenses for the CNCF allowlist license policy.
• It would help if we needed to potentially share code with libbpf in the future (libbpf is LGPL-2.1 OR BSD-2-Clause).
• "Dual BSD/GPL" has the additional advantage of being a valid license string in the eyes of the Linux kernel verifier.

For more details, please refer to https://github.com/cilium/cilium/issues/18823

[LiZhenCheng9527]

/assign

[hzxuzhonghu]

Fixed