Fix garbled java class name problem of uobjnew.py

After this fix, the output may look like this:
NAME/TYPE                      # ALLOCS      # BYTES
[B                                    1         1016
[D                                    1         8016

tools/lib/uobjnew.py

@@ -96,9 +96,11 @@
  struct key_t key = {};
  struct val_t *valp, zero = {};
  u64 classptr = 0, size = 0;
+ u32 length = 0;
  bpf_usdt_readarg(2, ctx, &classptr);
+ bpf_usdt_readarg(3, ctx, &length);
  bpf_usdt_readarg(4, ctx, &size);
- bpf_probe_read_user(&key.name, sizeof(key.name), (void *)classptr);
+ bpf_probe_read_user(&key.name, min(sizeof(key.name), (size_t)length), (void *)classptr);
  valp = allocs.lookup_or_try_init(&key, &zero);
  if (valp) {
  valp->total_size += size;