Product definition template 31.

This PR includes pdt 31 coverage for the new GRIB2 functionality.
I though that too ... however the GRIB spec for PDT 4.31 - satellite, states that `Scaled value of central wave number of band nb (units: m-1)` for octets `(22+11(nb-1))-(25+11(nb-1))`

Am I misinterpreting this?