I'm going through a PCI hardening document and they recommend "only five concurrent SSH sessions when connecting to the system".
I remember encountering same issue and dealing with it by means of QoS:
1. Enable QoS on the gateway
2. Create a rule on top of default QoS rule
3. Specify ssh as service and define destinations as your gateways or management servers BEHIND gateways
4. Right-click "Action" field of the rule and click "Edit Settings"
5. Click "Advanced"
6. Change setting as per this screenshot:
7. Add tracking options to the rule and apply the policy:
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