r8152: fix the poor throughput for 2.5G devices

Fix the poor throughput for 2.5G devices, when changing the speed from
auto mode to force mode. This patch is used to notify the MAC when the
mode is changed.

Fixes: 195aae32 ("r8152: support new chips")
Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>