Both tests in the conditional depend on the
qnetworkinterface feature, and will fail to build
if qt is configured without the networkinterface feature.
Additionally, a missing system header in a test was added.
Change-Id: Ife5989ee57675ebe117de2c92a4f96c7125cbab1
Pick-to: 6.3
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>