generate_packets.py: Move field comparison into type code
Part of #45206. Make Field.get_cmp() a wrapper around a call to FieldType.get_code_cmp() that compares fields as appropriate. Note that in order to reuse the cmp of simpler types, this will result in changes to array cmp code.
Part of #45206. Make Field.get_cmp() a wrapper around a call to FieldType.get_code_cmp() that compares fields as appropriate. Note that in order to reuse the cmp of simpler types, this will result in changes to array cmp code.