tools: bpftool: dual license all files

Currently bpftool contains a mix of GPL-only and GPL or BSD2
licensed files.  Make sure all files are dual licensed under
GPLv2 and BSD-2-Clause.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Sean Young <sean@mess.org>
Acked-by: Jiri Benc <jbenc@redhat.com>
Acked-by: David Calavera <david.calavera@gmail.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Joe Stringer <joe@wand.net.nz>
Acked-by: David Ahern <dsahern@gmail.com>
Acked-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Acked-by: Petar Penkov <ppenkov@stanford.edu>
Acked-by: Sandipan Das <sandipan@linux.ibm.com>
Acked-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Taeung Song <treeze.taeung@gmail.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
CC: okash.khawaja@gmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/btf_dumper.c

-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /* Copyright (c) 2018 Facebook */
 
 #include <ctype.h>

tools/bpf/bpftool/cgroup.c

-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (C) 2017 Facebook
 // Author: Roman Gushchin <guro@fb.com>
 

tools/bpf/bpftool/jit_disasm.c

+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /*
  * Based on:
  *

tools/bpf/bpftool/json_writer.c

+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /*
  * Simple streaming JSON writer
  *

tools/bpf/bpftool/json_writer.h

+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
 /*
  * Simple streaming JSON writer
  *

tools/bpf/bpftool/map_perf_ring.c

-// SPDX-License-Identifier: GPL-2.0-only
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /* Copyright (C) 2018 Netronome Systems, Inc. */
 /* This program is free software; you can redistribute it and/or
  * modify it under the terms of version 2 of the GNU General Public

tools/bpf/bpftool/net.c

-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (C) 2018 Facebook
 
 #define _GNU_SOURCE

tools/bpf/bpftool/netlink_dumper.c

-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (C) 2018 Facebook
 
 #include <stdlib.h>

tools/bpf/bpftool/netlink_dumper.h

-/* SPDX-License-Identifier: GPL-2.0+ */
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
 // Copyright (C) 2018 Facebook
 
 #ifndef _NETLINK_DUMPER_H_

tools/bpf/bpftool/perf.c

-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (C) 2018 Facebook
 // Author: Yonghong Song <yhs@fb.com>