pypy3 didn't support ctypes bit-fields

https://github.com/iovisor/bcc/blob/35cb9fd1cb0884e7a1fed1d3c01314655e40482c/src/python/bcc/disassembler.py#L26-L33

`BPFInstrFields` create fields with bit-fields, causing pypy binding failed.

```python
for item in typedict.get('_anonymous_', []):
if item not in dict(typedict['_fields_']):
raise AttributeError("Anonymous field not found")
```

Raising ValueError:

```
>>>> dict(['a', 'b', 'c'])
Traceback (most recent call last):
File "", line 1, in
ValueError: sequence of pairs expected
```

I do a workaround with remove bit-fields and it works fine (in my case). Will it cause some issue?

Thanks.

Read src/python/bcc/disassembler.py at lines 26-33 and reproduce the PyPy3 binding failure involving BPFInstrFields bit-fields and the shown dict conversion. Compare the reported workaround with the existing ctypes definition; done means the PyPy binding loads successfully without breaking the disassembler's field behavior.

Written by the indexing model from the issue text.