Use AppOpsManager#setUidMode instead of #setMode

Security related app-ops should be set with AppOpsManager#setUidMode
instead of AppOpsManager#setMode.

Test: manual - toggle All Files Access for a test app, reboot device and
observe in /data/system/appops.xml that the mode was for UID instead of
package
Test: ensure that the right state is reflected in the relevant Settings
activities

Change-Id: I261953ff88bc049cf0a2f04f8caac00b8cc6f704