Function register_app 

pub unsafe extern "C" fn register_app(
    app_id: &Id,
    description: *const c_char,
    desc_len: usize,
) -> ReturnValue

Register an application in the daemon.

• @param app_id four byte long character array with the application id
• @param description long name of the application
• @param desc_len strlen of the description
• @return Value from DltReturnValue enum