Add dns signal count into validation log for debugging

Dns signal may need to reevaluate the threshold if force
reevaluation is triggered and actually a stall. Provide dns
signal count while force reevaluation is triggered to help
debugging.

Bug: 113916551
Test: atest NetworkStackTests
Change-Id: Ia762752a41a4bb78ba9844917cbede7aeb2f0fc2