Including DStypes GaugeInc and GaugeAdd for tail plugin

Hi, we've created GaugeInc and GaugeAdd DSTypes for tail plugin to get raw numbers of match expressions, I think that can be useful for tail plugin users
These are bit-fields. The new numbers thus have to be 0x10 and 0x20 (decimal 16 and 32). However, UTILS_MATCH_DS_TYPE_* seems to be stored in the same bit field (unless I missed s/th in a quick check), so those would have to be changed accordingly as well (I think you can make them 0x1000, 0x2000, etc.). Also, while you're at it, it might be good to add a comment explaining how these defines work ;-)