generate_packets.py: ignore key fields for differ_used
For any delta-enabled, non-is-info packets that both have a (non-boolean) key field and only boolean fields (folded into header) otherwise, differ_used is True, when it should be False ~> decide it off of self.other_fields instead of self.fields.
For any delta-enabled, non-is-info packets that both have a (non-boolean) key field and only boolean fields (folded into header) otherwise, differ_used is True, when it should be False ~> decide it off of self.other_fields instead of self.fields.