r8169: fix auto speed down issue

r8169: fix auto speed down issue

commit e2409d83434d77874b461b78af6a19cd6e6a1280 upstream.

It would cause no link after suspending or shutdowning when the
nic changes the speed to 10M and connects to a link partner which
forces the speed to 100M.

Check the link partner ability to determine which speed to set.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>