Device behavior analysis shows that parameter position.valid can not be applied to Digita-matter devices. They only show position type is 2d fix, 3d fix (currently stored as position.fix.type), and old fix (due to loss of signal) now stored in boolean parameter position.outdated=true
parameter position.valid removed from the protocol implementation
also added parameter gsm.network.type.enum storing the raw value used in gsm.network.type. It is useful when the parameter gsm.network.type mapping can not be resolved based on the existing documentation