NIC Bonding in FreePBX 13

Dear All,

I have been using NIC bonding in FreePBX 12 for a long time. Without NetworkManager, I created entries in /etc/sysconfig/network-scripts, one for each NIC to be a slave, one bond as a master and one bride carrying the IP address of the NIC team - the old fashioned way. This did work without any issues. Reading other posts on this subject matter: No, I do not need the bandwidth, but the FreePBX box (Supermicro Atom board) is connected to two stacked switches, so why not take the potential upside in availability if all it costs is one ethernet cable.

Migrating to FreePBX 13, this solution does no longer work. The migrated configuration creates problems and creating a new bond in FreePBX SystemAdmin does not seem to work either. Upon opening the terminal, the following error message is shown in red (after the colon, this is my translation back into English):

file_get_contents(/sys/class/net/bonding_masters/type): failed to open stream: file or directory not found

It seems like one would now be forecd to use sysfs for bonding. As far as I understand, this is difficult to make persistent. Can someone please point me to how to achieve NIC bonding in FreePBX 13?