[Thinkit] Update ThinKit to return StubInterface for unit test mocking, Add SupportsSendPacket to ControlDevice interface, Enhanced the error logging in link_flap_test. Fixed peer_interface format mismatch issue, Improved naming: Device() -> ControlDevice(), Added multiple control devices to generic testbed & Added peer_device_index to InterfaceInfo in GenericTestbed and added multiple host control device feature to generic test fixture.

[Thinkit] Update ThinKit to return StubInterface for unit test mocking, Add SupportsSendPacket to ControlDevice interface, Enhanced the error logging in link_flap_test. Fixed peer_interface format mismatch issue, Improved naming: Device() -> ControlDevice(), Added multiple control devices to generic testbed & Added peer_device_index to InterfaceInfo in GenericTestbed and added multiple host control device feature to generic test fixture. #1999