Cherrypick 1.26: use subnets of ensured NLBs when update worker node SG rules

[oliviassss]

What type of PR is this?

Uncomment only one, leave it on its own line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
see #763
Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[cartermckinnon]

/lgtm
/approve

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