Custom OPC UA types: define a constant for the associated namespace index

Description

Define a constant global variable to indentify in which namespace index custom types are stored.

Code version identification

sha1: f7dc764a

Current behavior

Currently a magic number is supplied in C files generated by gen-sopc-types.py to indicate namespace indexes associated to an encodeable type.

Expected behavior

We should use an explicit variable to identify the namespace index associated to an encodeable type. For example if we generate a file with prefix Custom and namespace 2, we can define a macro #define SOPC_CUSTOM_NS_INDEX 2 which is referenced in implementation instead of 2.

Security impact

N.A

Implementation

Script gen-sopc-types.py should dynamically generate the variable and reference using an explicit variable to identify namespace index.