[Voice Update] Sync default voice debug level with upstream.

indra/newview/app_settings/settings.xml

@@ -16606,7 +16606,7 @@ This should be as low as possible, but too low may break functionality</string>
       <key>Type</key>
       <string>String</string>
       <key>Value</key>
-      <string>-1</string>
+      <string>0</string>
     </map>
     <key>VivoxDebugSIPURIHostName</key>
     <map>

indra/newview/llvoicevivox.cpp

@@ -839,7 +839,7 @@ void LLVivoxVoiceClient::stateMachine()
 						std::string loglevel = gSavedSettings.getString("VivoxDebugLevel");
 						if(loglevel.empty())
 						{
-							loglevel = "-0";	// turn logging off completely
+							loglevel = "0";	// turn logging off completely
 						}
 
 						args += " -ll ";