Turn auto attach on/off when we attach/detach.

Some network operators will detach after a timeout period, isDataAllowed()
will not allow a data connection because mAutoAttachOnCreation is false
and gprsState is not STATE_IN_SERVICE.  This change toggles
mAutoAttachOnCreation based on attach/detach events and data will be
allowed if gprsState == STATE_IN_SERVICE or mAutoAttachOnCreation.

Bug: 7491805
Change-Id: If41c2514ebdb9cd2fba88eef692f2c7160c04b0f