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### Description of PR
adjust test_techsupport.py to support IPv6
* fixed mirroring fixture when ipv6 only topo is used
* verified cmd to check is supported with new topo

Summary:
Fixes # (issue)

### Type of change

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- e.g.
- [x] Bug fix
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- [ ] Bug fix
- [x] Testbed and Framework(new/improvement)
- [] New Test case
    - [ ] Skipped for non-supported platforms
- [ ] Test case improvement

### Back port request
- [ ] 202205
- [ ] 202305
- [ ] 202311
- [ ] 202405
- [] 202411
- [x] 202505

### Approach
#### What is the motivation for this PR?
testing ipv6 only topology

#### How did you do it?
Adjusted the test to handle this topology,

#### How did you verify/test it?
internal regression

#### Any platform specific information?

#### Supported testbed topology if it's a new test case?

### Documentation
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Link to the wiki page?
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