unwinder/native: Log vDSO segments

Unwinding through vDSO regions is not supported yet. We need to open the
non-file memory mapping and retrieve its unwind info, but until it's
implemented let's log with the right message.

The mapping types will probably disappear, that's why I am not bothering
with extracting them into a constant or enum.

src/bpf/profiler.bpf.c

@@ -340,7 +340,7 @@ int dwarf_unwind(struct bpf_perf_event_data *ctx) {
     }
 
     if (mapping->type == 2) {
-      LOG("JIT section, stopping");
+      LOG("vDSO section, stopping");
       return 1;
     }