nat: T6345: source NAT port mapping "fully-random" is superfluous in Kernel >=5.0 (backport #3507)

[mergify]

Change Summary

random - In kernel 5.0 and newer this is the same as fully-random. In earlier kernels the port mapping will be randomized using a seeded MD5 hash mix using source and destination address and destination port.

https://git.netfilter.org/nftables/commit/?id=fbe27464dee4588d906492749251454

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6345

Related PR(s)

Component(s) name

NAT

Proposed changes

How to test

Smoketest result

cpo@LR1.wue3:~$ /usr/libexec/vyos/tests/smoke/cli/test_nat.py
test_dnat (__main__.TestNAT.test_dnat) ... ok
test_dnat_negated_addresses (__main__.TestNAT.test_dnat_negated_addresses) ... ok
test_dnat_redirect (__main__.TestNAT.test_dnat_redirect) ... ok
test_dnat_without_translation_address (__main__.TestNAT.test_dnat_without_translation_address) ... ok
test_nat_balance (__main__.TestNAT.test_nat_balance) ... ok
test_nat_no_rules (__main__.TestNAT.test_nat_no_rules) ... ok
test_snat (__main__.TestNAT.test_snat) ... ok
test_snat_groups (__main__.TestNAT.test_snat_groups) ... ok
test_snat_net_port_map (__main__.TestNAT.test_snat_net_port_map) ... ok
test_snat_required_translation_address (__main__.TestNAT.test_snat_required_translation_address) ... ok
test_static_nat (__main__.TestNAT.test_static_nat) ... ok

----------------------------------------------------------------------
Ran 11 tests in 54.925s

OK

make testc reports

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

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This is an automatic backport of pull request #3507 done by [Mergify](https://mergify.com).