Add FLAG_IMMUTABLE to PendingIntents

Test: atest BugreportManagerTest#normalFlow_wifi
Fixes: 209527579
Bug: 176094662
Bug: 194696395
Change-Id: I4b78f32ceda32f2c32f2b4f6ade6e3fe0398e901
(cherry picked from commit f2c3731d4d48deee414551cf522b1317de3b29a5)
3 files changed