use port I/O instead of memory mapped I/O

In an attempt to avoid the alledged  "write post bug", I'm trying
port I/O instead of memorymapped. I also notice that version 1.3
of the RealTek RTL8139D data sheet states that one must write a one
to the Interrupt Status register inorder to ack that interrrupt.
Writing a zero has no effect.
change timer message.