Allows to get how many user there are on the given group.
INVOCATION METHOD: This function allows to perform an synchronous remote invocation. for the service "af_kernel::af_user::af_group_num_elements".
This function is a synchronous version for afdal_af_kernel_af_user_af_group_num_elements function.
|af_group_id ||Group id to be used to count how many users there are. |