of12 adapt a test after set_ipv4_src_masked change
of12 ofpmatch: don't forget to decode field values
of12 use None for no-mask
of12 ofpmatch: don't forget to decode field masks too
test_parser_v12 abuse this to test to_jsondict and from_jsondict
of12  remove automatic-mask functionality for now
test_parser_v12 adapt to mask=None changes
of12 adapt tests: removal of special handling for UINT32_MAX etc mask values
of12 adapt tests: remove automatic mask