sync to latest libbpf

sync to libbpf v0.0.8. Add newer helpers to
helpers.h, libbpf.c error reporting and docs.
diff --git a/introspection/bps.c b/introspection/bps.c
index c5984c4..97868f7 100644
--- a/introspection/bps.c
+++ b/introspection/bps.c
@@ -45,6 +45,7 @@
   [BPF_PROG_TYPE_TRACING] = "tracing",
   [BPF_PROG_TYPE_STRUCT_OPS] = "struct_ops",
   [BPF_PROG_TYPE_EXT] = "ext",
+  [BPF_PROG_TYPE_LSM] = "lsm",
 };
 
 static const char * const map_type_strings[] = {