libbpf: Bump current version to v0.0.6

New release cycle started, let's bump to v0.0.6 proactively.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20190930222503.519782-1-andriin@fb.com

tools/lib/bpf/libbpf.map

@@ -190,3 +190,6 @@ LIBBPF_0.0.5 {
 	global:
 		bpf_btf_get_next_id;
 } LIBBPF_0.0.4;
+
+LIBBPF_0.0.6 {
+} LIBBPF_0.0.5;