Require MODIFY_PHONE_STATE for preferred TTY mode

Now that ACTION_TTY_PREFERRED_MODE_CHANGED is no longer a protected
broadcast, require the sender to have MODIFY_PHONE_STATE.

Bug: 169196062
Test: atest TelecomManagerTest, manual
Change-Id: I9e16429e25faa326dfa1f93284c34346573320ee
1 file changed