CSocket: Don't create the read notifier until after we've connected

This makes it so that "on_connected" always gets called first.
Since accepted sockets are connected before construction, they have
to manually set CSocket::m_connected.

Libraries/LibCore/CSocket.h

@@ -51,6 +51,7 @@ protected:
 private:
     virtual bool open(CIODevice::OpenMode) override { ASSERT_NOT_REACHED(); }
     bool common_connect(const struct sockaddr*, socklen_t);
+    void ensure_read_notifier();
 
     Type m_type { Type::Invalid };
     RefPtr<CNotifier> m_notifier;