fix tbcd decoding

[hishamanver]

fixes the decode_from_tbcd() method calls for the MsisdnAVP and StnSrAVP

additionally have some whitespace cleanup (my editor does this automatically, but i can remove if required)

Before

>>> ula.subscription_data_avp.msisdn_avp.decode()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.9/site-packages/bromelia/avps/etsi_3gpp/ts_129_329.py", line 48, in decode
    return decode_from_tbcd(self.data)
  File "/usr/local/lib/python3.9/site-packages/bromelia/utils.py", line 246, in decode_from_tbcd
    if "f" not in bits:
TypeError: a bytes-like object is required, not 'str'

>>> ula.subscription_data_avp.stn_sr_avp.decode()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.9/site-packages/bromelia/avps/etsi_3gpp/ts_129_272.py", line 65, in decode
    return decode_from_tbcd(self.data)
  File "/usr/local/lib/python3.9/site-packages/bromelia/utils.py", line 246, in decode_from_tbcd
    if "f" not in bits:
TypeError: a bytes-like object is required, not 'str'

After

>>> ula.subscription_data_avp.stn_sr_avp.decode()
'61418070329'
>>> ula.subscription_data_avp.msisdn_avp.decode()
'61000000000'