Fixed data disconnected for 10 seconds when disabling tethering

Before we always tear down the tethering data connection even
though the same data connection could be used for other
purposes (e.g. internet, mms). Now we don't do that if the
data connection can be shared for other purposes. Note that
we only do this for non-CDMA case.

Bug: 132322044
Bug: 131930219
Bug: 129387119

Test: Manual
Change-Id: I4061c4b86c09718d834a5dc16d24c52ed7801b0f