Modified TC5 final port up check as timing was causing flaky results

[mastarkey]

This PR increases the final verification wait time in the TC5 "short down" scenario from 10 seconds to 30 seconds. The README does not mandate strict upper limits for this step, only that the interface should be stable after the short down event. Extending the wait time provides a sufficient buffer to confirm that the DUT has fully settled in the "UP" state, reducing test flakiness without violating any documented requirements.

[OpenConfigBot]

Pull Request Functional Test Report for #3662 / ba05c4f

Virtual Devices

Device	Test	Test Documentation	Job	Raw Log
Arista cEOS		RT-5.5: Interface hold-time
Cisco 8000E		RT-5.5: Interface hold-time
Cisco XRd		RT-5.5: Interface hold-time
Juniper ncPTX		RT-5.5: Interface hold-time
Nokia SR Linux		RT-5.5: Interface hold-time
Openconfig Lemming		RT-5.5: Interface hold-time

Hardware Devices

Device	Test	Test Documentation	Raw Log
Arista 7808		RT-5.5: Interface hold-time
Cisco 8808		RT-5.5: Interface hold-time
Juniper PTX10008		RT-5.5: Interface hold-time
Nokia 7250 IXR-10e		RT-5.5: Interface hold-time

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