fix(nodeadm): calculate max pods on default network card

[mselim00]

Issue #, if available:

Description of changes:

At the moment there's a gap between the max pods value from eni-max-pods.txt and the fallback calculator for multicard instance types.

Both use the equation max # network interfaces * (max # ipv4 addresses per interface -1) + 2 for the max pods value, but the text file is calculated using the max number of network interfaces for the default network card, whereas the fallback uses the total maximum number of network interfaces for the instance. To take an example, consider p4de.24xlarge

$ aws ec2 describe-instance-types --region=us-west-2 --instance-type=p4d.24xlarge | jq '.InstanceTypes[].NetworkInfo'
{
  "NetworkPerformance": "4x 100 Gigabit",
  "MaximumNetworkInterfaces": 60,
  "MaximumNetworkCards": 4,
  "DefaultNetworkCardIndex": 0,
  "NetworkCards": [
    {
      "NetworkCardIndex": 0,
      "NetworkPerformance": "100 Gigabit",
      "MaximumNetworkInterfaces": 15,
      "BaselineBandwidthInGbps": 100,
      "PeakBandwidthInGbps": 100
    },
    {
      "NetworkCardIndex": 1,
      "NetworkPerformance": "100 Gigabit",
      "MaximumNetworkInterfaces": 15,
      "BaselineBandwidthInGbps": 100,
      "PeakBandwidthInGbps": 100
    },
    {
      "NetworkCardIndex": 2,
      "NetworkPerformance": "100 Gigabit",
      "MaximumNetworkInterfaces": 15,
      "BaselineBandwidthInGbps": 100,
      "PeakBandwidthInGbps": 100
    },
    {
      "NetworkCardIndex": 3,
      "NetworkPerformance": "100 Gigabit",
      "MaximumNetworkInterfaces": 15,
      "BaselineBandwidthInGbps": 100,
      "PeakBandwidthInGbps": 100
    }
  ],
  "Ipv4AddressesPerInterface": 50,
  "Ipv6AddressesPerInterface": 50,
  "Ipv6Supported": true,
  "EnaSupport": "required",
  "EfaSupported": true,
  "EfaInfo": {
    "MaximumEfaInterfaces": 4
  },
  "EncryptionInTransitSupported": true,
  "EnaSrdSupported": false
}

eni-max-pods.txt shows 737, which follows from NetworkCards[DefaultNetworkCardIndex].MaximumNetworkInterfaces * (Ipv4AddressesPerInterface - 1) + 2 = 15 * (50 - 1) + 2 = 737. On the other hand, the calculator fallback currently uses MaximumNetworkInterfaces * (Ipv4AddressesPerInterface - 1) + 2 = 60 * (50 - 1) + 2 = 2,942.

The max pods value is mainly intended to account for the fact that the VPC CNI only allocates pods using the first network interface. Since this calculator is only used if no corresponding value was found in the text file for the instance type, the existing math could also lead to a major discrepancy between AMI versions for new instance types.

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Testing Done

Added a unit test for a mock multi-card instance type.

See this guide for recommended testing for PRs. Some tests may not apply. Completing tests and providing additional validation steps are not required, but it is recommended and may reduce review time and time to merge.

[cartermckinnon]

The max pods value is mainly intended to account for the fact that the VPC CNI only allocates pods using the first network interface.

@jaydeokar is working on removing this limitation, so we can't bake this assumption in.

[mselim00]

Absorbed into https://github.com/awslabs/amazon-eks-ami/pull/2446

The VPC CNI has yet to implement support for allocating on multiple ENIs, and even when it does, the fallback should line up with the default values and allow custom configurations for those using that version + feature of the VPC CNI.