[Thread] make InfraInterfaceController mockable

It's generally discouraged to mock a static method, so this commit
changes InfraInterfaceController#createIcmp6Socket to non-static method
and inject InfraInterfaceController into ThreadNetworkControllerService
as an external dependency.

Bug: 317555104
Change-Id: I6f88c02858279223684c781dc065a9bf84ae15ab