r8169: keep pause settings on interface down/up cycle

Currently, if the user changes the pause settings, the default settings
will be restored after an interface down/up cycle, and also when
resuming from suspend. This doesn't seem to provide the best user
experience. Change this to keep user settings, and just ensure that in
jumbo mode pause is disabled.
Small drawback: When switching back mtu from jumbo to non-jumbo then
pause remains disabled (but user can enable it using ethtool).
I think that's a not too common scenario and acceptable.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>