C2MS12 — Non-sensical Description for PROD-MSGS-TO-SEND

In Product Response Message, PROD-MSGS-TO-SEND field is an unsigned type, with a stated minimum "value" of 0+, but says in the description text the following:

A value of “-1” can be used to indicate “Unknown”.

Should probably find a different way to indicate unknown, such as not including this optional field in the message.

Clarify description for PROD-MSGS-TO-SEND field

Update the notes for the PROD-MSGS-TO-SEND field of the Product Response Message to indicate that the field should not be included if the number of messages is unknown.