audio policy: re enable setForceUse for system apps.

Some system apps (not having system AIDs) still need this
hidden API due to lack of better option for media use case routing.

Add protection by privileged permission MODIFY_AUDIO_ROUTING instead.

Bug: 79475856
Test: manual regression for music playback over speaker and bluetooth
Change-Id: Icaa585a9fa4c043c291f24c9bab4a93f02406955
diff --git a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
index 008d655..b75b234 100644
--- a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
+++ b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
@@ -121,9 +121,11 @@
     if (mAudioPolicyManager == NULL) {
         return NO_INIT;
     }
-    if (!settingsAllowed()) {
+
+    if (!modifyAudioRoutingAllowed()) {
         return PERMISSION_DENIED;
     }
+
     if (usage < 0 || usage >= AUDIO_POLICY_FORCE_USE_CNT) {
         return BAD_VALUE;
     }