bpf: Relicense disassembler as GPL-2.0-only OR BSD-2-Clause

Some time ago we dual-licensed both libbpf and bpftool through commits
1bc38b8f ("libbpf: relicense libbpf as LGPL-2.1 OR BSD-2-Clause")
and 907b2236 ("tools: bpftool: dual license all files"). The latter
missed the disasm.{c,h} which we pull in via kernel/bpf/ such that we
have a single source for verifier as well as bpftool asm dumping, see
also f4ac7e0b ("bpf: move instruction printing into a separate file").
It is currently GPL-2.0-only and missed the conversion in 907b2236,
therefore relicense the two as GPL-2.0-only OR BSD-2-Clause as well.

Spotted-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Brendan Jackman <jackmanb@google.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>