sync with latest libbpf (#2594)

The following helpers are sync'ed into bcc and will
be available in linux 5.5.
  bpf_probe_read_kernel
  bpf_probe_read_kernel_str
  bpf_probe_read_user
  bpf_probe_read_user_str

Signed-off-by: Yonghong Song <yhs@fb.com>
diff --git a/introspection/bps.c b/introspection/bps.c
index 5e510aa..5916093 100644
--- a/introspection/bps.c
+++ b/introspection/bps.c
@@ -42,6 +42,7 @@
   [BPF_PROG_TYPE_CGROUP_SYSCTL] = "cgroup_sysctl",
   [BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE] = "raw_tracepoint_writable",
   [BPF_PROG_TYPE_CGROUP_SOCKOPT] = "cgroup_sockopt",
+  [BPF_PROG_TYPE_TRACING] = "tracing",
 };
 
 static const char * const map_type_strings[] = {