Support negative prefix length in the `cidr`, `cidr4`, `cidr6`, `ipmask`,
`ipmask4` and `ipmask6` data types when an optional truish flag is passed
to the datatype name.
Ref: #4812
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit cd06e708d8d8037486b77dab3389ca91a88f2dd0)