Fix: removed volatile modifier

volatile modifier is not needed to synchronize access to the variables.
In this use case the compiler will make changes to these variables
visible to other threads.

MobileLibrary/iOS/PsiphonTunnel/PsiphonTunnel/PsiphonTunnel.m

@@ -46,13 +46,13 @@
     dispatch_queue_t callbackQueue;
     dispatch_semaphore_t noticeHandlingSemaphore;
 
-    volatile _Atomic PsiphonConnectionState connectionState;
+    _Atomic PsiphonConnectionState connectionState;
 
-    volatile _Atomic NSInteger localSocksProxyPort;
-    volatile _Atomic NSInteger localHttpProxyPort;
+    _Atomic NSInteger localSocksProxyPort;
+    _Atomic NSInteger localHttpProxyPort;
 
     Reachability* reachability;
-    volatile _Atomic NetworkStatus currentNetworkStatus;
+    _Atomic NetworkStatus currentNetworkStatus;
 
     BOOL tunnelWholeDevice;
 
@@ -61,7 +61,7 @@
     NSString *secondaryGoogleDNS;
 
     
-    volatile _Atomic BOOL useInitialDNS; // initialDNSCache validity flag.
+    _Atomic BOOL useInitialDNS; // initialDNSCache validity flag.
     NSArray<NSString *> *initialDNSCache;  // This cache becomes void if internetReachabilityChanged is called.
 }