Don't allow Guest user to bypass permission check

Fix an issue where Guest can bypass addNetwork permission check with
SYSTEM_ALERT_WINDOW permission.

Bug: 255537598
Test: atest com.android.server.wifi
Change-Id: I1526944d1d2c67db83d20137f5b98fead64d331c
Merged-In: I1526944d1d2c67db83d20137f5b98fead64d331c
(cherry picked from commit 6c8e32237668d1e4c9329d76729f38bcd0bb287e)
2 files changed