Retain protected members in proguard rule.

Bug: 215186421
Test: build and atest FrameworksTelephonyTests
Change-Id: I70035c8cdc55a6ef35882812e33eef1deae1a8d3
diff --git a/proguard.flags b/proguard.flags
index 04040a7..ebc8922 100644
--- a/proguard.flags
+++ b/proguard.flags
@@ -9,7 +9,7 @@
 public *;
 }
 -keepclasseswithmembers class android.telephony.gsm.SmsMessage,android.telephony.gsm.SmsMessage$* {
-public *;
+public protected *;
 }
 
 # Keep telephony sysprop
@@ -17,9 +17,9 @@
 public *;
 }
 
-# Keep public classes and members
+# Keep public classes and public/protected members
 -keepclasseswithmembers class com.android.internal.telephony.** {
-public *;
+public protected *;
 }
 
 # Keep classes and members that have the @UnsupportedAppUsage annotation