Remove unnecessary friends of NetworkInterface

Author: kjbracey

features/netsocket/NetworkInterface.h

@@ -421,12 +421,6 @@ class NetworkInterface: public DNS {
 #if !defined(DOXYGEN_ONLY)
 
 protected:
-    friend class InternetSocket;
-    friend class UDPSocket;
-    friend class TCPSocket;
-    friend class TCPServer;
-    friend class SocketAddress;
-
     friend NetworkStack *_nsapi_create_stack(NetworkInterface *iface, std::false_type);
 
     /** Provide access to the NetworkStack object