r8169: adjust __rtl8169_set_features

Remove the "changed" test in __rtl8169_set_features(). Instead, do
simple test in rtl8169_set_features().

Set the RxChkSum and RxVlan through __rtl8169_set_features() in
rtl_open().

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>