usbnet: mcs7830: rework link state detection

usbnet: mcs7830: rework link state detection

Even with the quirks in commit dabdaf0c (mcs7830: Fix link state
detection) there are still spurious link-down events for some chips
where the false link-down events count go over a few hundreds.

This patch takes a more conservative approach and only looks at
link-down events where the link-down state is not combined with other
states (e.g. half/full speed, pending frames in SRAM or TX status
information valid). In all other cases we assume the link is up.

Tested on MCS7830CV-DA (USB ID 9710:7830).

Cc: Ondrej Zary <[email protected]>
Cc: Michael Leun <[email protected]>
Cc: Ming Lei <[email protected]>
Signed-off-by: Octavian Purdila <[email protected]>
Signed-off-by: David S. Miller <[email protected]>