The SQL* helpers are meant to always set the `Valid` field of the
sql.Null* type to true. Otherwise they cannot be used to set a valid,
empty field. However, we dont want to break the behaviour of the
existing SQLStr helper and so this commit adds a new helper with the
desired functionality.
Here we start using the newly added message_flags and channel_flags
columns of the channel_policies table. The test added previoulsy to
demonstrate the bug is now updated to show that the bug has been fixed.
