Added FLAG_IMMUTABLE flag for security purposes

Prevent the intent to be altered by the maleware.

Bug: 155094269
Test: Telephony sanity tests

Merged-In: Ice6e438eb437d377f8c5f26891938302fcb0c8d4
Change-Id: Ice6e438eb437d377f8c5f26891938302fcb0c8d4
(cherry picked from commit 21e03356)