I've added support for software selection of the AUI or BNC connectors
for boards which can use it.  This is done with the `link0' flag to
ifconfig(8).  By default it will come up with the previous setting,
which will be the one set by EZSETUP in non-volatile memory after a
cold reset.

To select AUI:

   ifconfig ed0 link0

To select BNC:

   ifconfig ed0 -link0

As far as I know, UTP should work in either mode.


Also, I've changed the driver to enable and disable shared memory
access as appropriate on *all* boards.  This probably isn't necessary,
but it shouldn't hurt.


As always, let me know if you have any problems.


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