Fixes deletion order in CC32xx socket shutdown. (#442)

This change ensures that threads higher priority than the closing call
have a chance to exit their kernel processing before the socket object
gets deleted.

This makes #440 slightly better.

src/freertos_drivers/net_cc32xx/CC32xxSocket.cxx

@@ -755,8 +755,8 @@ int CC32xxSocket::close(File *file)
         portENTER_CRITICAL();
         remove_instance_from_sd(sd);
         portEXIT_CRITICAL();
-        delete this;
         sl_Close(sd);
+        delete this;
     }
     else
     {