-- binary
04 01 # version / type
00 0f # length
12 34 56 78 # xid
00 04 # err_type
00 08 # code
61 62 63 # data
-- python
ofp.message.error_msg(
    xid=0x12345678,
    err_type=ofp.OFPET_BAD_MATCH,
    code=ofp.OFPBMC_BAD_MASK,
    data="abc")