perftune.py: identify and configure ENA Express NICs (on AWS machines)

[mykaul]

From https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ena-express.html :
Benefits of ENA Express
Increases the maximum bandwidth a single flow can use from 5 Gbps to 25 Gbps within the Availability Zone, up to the aggregate instance limit.

Reduces tail latency of network traffic between EC2 instances, especially during periods of high network load.

Detects and avoids congested network paths.

Handles some tasks directly in the network layer, such as packet reordering on the receiving end, and most retransmits that are needed. This frees up the application layer for other work.

From https://docs.aws.amazon.com/ec2/latest/instancetypes/so.html#so_network , supported instances are :

i4i.8xlarge	18.75 Gigabit	✗	✓	✓	1	8	30	✓
i4i.12xlarge	28.12 Gigabit	✗	✓	✓	1	8	30	✓
i4i.16xlarge	37.5 Gigabit	✗	✓	✓	1	15	50	✓
i4i.24xlarge	56.25 Gigabit	✗	✓	✓	1	15	30	✓
i4i.32xlarge	75 Gigabit	✓	✓	✓	1	15	50	✓
i4i.metal	75 Gigabit	✓	✓	✓	1	15	50	✓

Enabling it - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ena-express-configure.html (I'm sure there's an API for it - but need to check of course).