Move AlertDialog to SYSTEM_ALERT

Move USSD alert dialog to SYSTEM_ALERT
so that it doesn't draw over other system
UI, such as the drop down menu.

Test: Manual
Bug: 63875994
Merged-In: I83b8b88439436c52543612b2b42ebd7952531525
Change-Id: I0664208729757a826c24725c8019f17c9c47ef77
1 file changed