[Mesh][eRPC] Callback server raise the wrong model index number when running 2 vendor model on the same element

• Git \ Installer version:
  • SDK : 5.20.00.43
• Test-Bed:
  • Power Consumption 
• Problem occurring %:
  • 100%
• Application:
  • ble5_simple_mesh_node_eRPC.hex
• Problem description:
  • An error occurs when using callbacks of model which it's index is different between two nodes.
    For example:
    Node A:

• Vendor Model - Index 0
• Generic Led On/Off - Index 1
  Node B:
• Generic Led On/Off - Index 0
• Vendor Model - Index 1

When Node A triggers a callback call for Node B (for example: button presses),
the eRPC raise the call for Generic LED On/Off (index 0) instead for Vendor Model (Index 1).

• Solution:
  • Modify bt_mesh_init_model_raw_init() so it will have one more opcode.
    Fill the last opcode of a model with 0 value.