include: dual license the bpf helper includes

The files bpf_api.h and bpf_elf.h are useful for TC BPF programs
to use. And there is no requirement that those be GPL only;
we intend to allow BSD licensed BPF helpers as well.

This makes the file license same as libbpf.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
diff --git a/include/bpf_api.h b/include/bpf_api.h
index 82c4708..5887d3a 100644
--- a/include/bpf_api.h
+++ b/include/bpf_api.h
@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0 or BSD-3-Clause */
 #ifndef __BPF_API__
 #define __BPF_API__
 
diff --git a/include/bpf_elf.h b/include/bpf_elf.h
index 84e8ae0..ea8a11c 100644
--- a/include/bpf_elf.h
+++ b/include/bpf_elf.h
@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0 or BSD-3-Clause */
 #ifndef __BPF_ELF__
 #define __BPF_ELF__