de2104x: fix ethtool

When the interface is up, using ethtool breaks it because:
a) link is put down but media_timer interval is not shortened to NO_LINK
b) rxtx is stopped but not restarted

Also manual 10baseT-HD (and probably FD too - untested) mode does not work -
the link is forced up, packets are transmitted but nothing is received.
Changing CSR14 value to match documentation (not disabling link check) fixes this.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Acked-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>