libbpf: add binary to gitignore

Some binaries are generated when building libbpf from tools/lib/bpf/,
namely libbpf.so.0.0.2 and libbpf.so.0.
Add them to the local .gitignore.
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/.gitignore

 libbpf_version.h
 FEATURE-DUMP.libbpf
 test_libbpf
+libbpf.so.*