Modify the way of obtaining get Wi-Fi connectivity

status to asynchronous API

Whether device is connected to internet via Wi-Fi network is used
to decide the eligibility of Carrier Roaming NB IoT NTN service.
If we get the capability information from synchronous API when
Wi-Fi signal lost, the capability does not report the latest value.

It was recommended to used asynchronous API to get the latest Wi-Fi connectivity status instead of using networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI)

Bug: 365035562
Flag: com.android.internal.telephony.flags.carrier_roaming_nb_iot_ntn
Test: atest TelephonyCountryDetectorTest
      manually test in live network to check whether Wi-Fi connection info is correct b/365035562#comment19 and comment20
Change-Id: Id05b1e81692c77934af5a9d265ef61b020705ec9