net: usb: sr9700: remove code to drive nonexistent MII

net: usb: sr9700: remove code to drive nonexistent MII

This device does not have a MII, even though the driver
contains code to drive one (because it originated as a copy of the
dm9601 driver). It also only supports 10Mbps half-duplex
operation (the DM9601 registers to set the speed/duplex mode
are read-only). Remove all MII-related code and implement
sr9700_get_link_ksettings which returns hardcoded correct
information for the link speed and duplex mode. Also add
announcement of the link status like many other Ethernet
drivers have.

Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Link: https://patch.msgid.link/20260113040649.54248-1-enelsonmoore@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>