fix: fix the service export condition

[zhiying-lin]

What type of PR is this?
/kind bug

What this PR does / why we need it:
use the serviceExport generation instead of service
Note: service does not have the generation.

Which issue(s) this PR fixes:

Fixes #

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

How has this code been tested

e2e tests passed, https://github.com/Azure/fleet-networking/actions/runs/13986059012

Special notes for your reviewer

The change should not break the mcs or atm, and they're using serviceImport instead of serviceExport.

[codecov]

Codecov Report

Attention: Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.26%. Comparing base (6c08b0b) to head (dbe2b2e).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/controllers/member/serviceexport/controller.go	96.77%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #281      +/-   ##
==========================================
+ Coverage   80.24%   80.26%   +0.01%     
==========================================
  Files          29       29              
  Lines        4020     4024       +4     
==========================================
+ Hits         3226     3230       +4     
  Misses        633      633              
  Partials      161      161              

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[michaelawyu]

LGTM, not counting other added comments ;)

[michaelawyu]

LGTM ;)