Don't report data stall for disconnected DataNetwork

Also check for DATA_STALL_RECOVERY_ON_BAD_NETWORK setting before
notifying validation state changed.

Test: atest DataNetworkControllerTest
Test: manual sanity; verified data is not affected
Bug: 229641474
Change-Id: Ia3a94642415ee4cf57ac5a90fa56d8f5efc9d5e3