I guess, "Indirect forwarding tunnels" are created by MME when at least one of AM mode bearer is created at target eNodeB. It is just created to achieve loss less handover. If you check the handover call flow, it is created only when target prepares the resource for a candidate UE.
If SGW is being changed as part of handover, MME may send "Created Indirect Data Forwarding Tunnel Request" to target SGW and MME receives response from target SGW.
Once the handover command message is sent out to UE, source eNodeB starts forwarding data to target eNodeB via direct link or indirect link.