Add reconnect with same session ID to iOS library

MobileLibrary/iOS/PsiphonTunnel/PsiphonTunnel/PsiphonTunnel.h

@@ -331,6 +331,19 @@ Swift: @code func onInternetReachabilityChanged(_ currentReachability: Reachabil
  */
 - (BOOL)start:(BOOL)ifNeeded;
 
+
+/*!
+ Force stops the tunnel and reconnects with the current session ID.
+ Retuns with FALSE immediately if no session ID has already been generated.
+
+ @note On the first connection `start:` method should always be used to generate a
+ session ID.
+
+ @return TRUE if the connection start was successful, FALSE otherwise.
+ Swift: @code func startWithCurrentSessionID() @endcode
+ */
+- (BOOL)stopAndReconnectWithCurrentSessionID;
+
 /*!
  Stop the tunnel (regardless of its current connection state).
  Swift: @code func stop() @endcode

MobileLibrary/iOS/PsiphonTunnel/PsiphonTunnel/PsiphonTunnel.m

@@ -149,6 +149,17 @@
     return [self start];
 }
 
+// See comment in header
+- (BOOL)stopAndReconnectWithCurrentSessionID {
+
+    // Proceed only if a session ID has alreaby been generated.
+    if (self.sessionID == nil) {
+        return FALSE;
+    }
+
+    return [self start];
+}
+
 /*!
  Start the tunnel. If the tunnel is already started it will be stopped first.
  Assumes self.sessionID has been initialized -- i.e., assumes that