Add checks for valid assembly instance numbers

Valid range for assembly numbers is 1 - 8000FFFF according to manual.
This is not checked in the set-config packet, nor is it checked during EIP_OBJECT_AS_REGISTER_REQ. Such checks should be added.

Furthermore: Equal assembly instance numbers for input/output should be rejected as well.
Presumably, this will only be done for the future minor release as we should avoid changes at API level.