Feature Request Overview (mandatory - Complete while in New status){_}
{}What user goal or problem do you need to solve?{_} 
Current neutron implementation enforces that security group is stateful.
However, we found that stateful security group has poor performance. Due to that, we introduce stateless security group.
This performance drop is significant in OVS-DPDK deployment(1/3 performance is reported from our customer).

Current implementation requires an additional option to make security group as stateless
 when SG is created.

If there is a performance benefits in stateless security group, stateless should be chosen as default and configurable in neutron configuration.

Business justification (mandatory - Complete while in New status)
How would this feature benefit the customer?
By this RFE, operator uses stateless SG as default for their tenant users and it will reduce the operational cost(investigating performance issue) by lacking stateless option by tenant users.
 
Functional requirements (mandatory - Complete while in New status){_}
{}What do you want the result of this feature to be? Add as many requirements as needed.{_}

•  neutron.conf has an option for stateless SG
•  SG is created without stateful option ensures the value is set in the option.

Describe the customer impact
We have a telco customer and they hit many performance issue. Then, they found that many cases tenant user uses statelful SGs.
They'd like to prevent this kind performance issue with their deployment configuration.

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(Optional) Point of contact

• Provide any additional points of contact for this feature request, such as an account executive, SA, or TAM: 
•  TAM