AudioPolicy/Flinger: harden security checks

Update list of methods which can only be called from system
components.

Bug: 162423060
Test: see poc
Change-Id: Ie266a2fdd31bdcecfe9c116596ae65a789b812c6
diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 6d96a8d..d442af6 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -4092,6 +4092,7 @@
     switch (code) {
         case TransactionCode::SET_MASTER_VOLUME:
         case TransactionCode::SET_MASTER_MUTE:
+        case TransactionCode::MASTER_MUTE:
         case TransactionCode::SET_MODE:
         case TransactionCode::SET_MIC_MUTE:
         case TransactionCode::SET_LOW_RAM_DEVICE: