smpp.pdu.pdu_types.DataCodingScheme.GSM_MESSAGE_CLASS very much exists,
and I can prove that manually in the python shell. So let's assume this
is a pylint bug and work around it
pySim/sms.py:72:21: E1101: Instance of 'DataCodingScheme' has no 'GSM_MESSAGE_CLASS' member (no-member)
Change-Id: Iab34bae06940fecf681af9f45b8657e9be8cbc7b