SamsungExynos3RIL: fix unable to swtich 2G/3G while connected to wifi

When connected to wifi, the actual mobile network is not connected
but mobile data is reported as enabled, causing the code to try
and disconnect, which never happens since it's not connected in the
first place. Fix by checking if the network is connected instead of
if it's enabled.

Change-Id: I291b739a26fbf6c10917f195f80ea5044b6da03c