r8152: set the RMS of RTL8153 according to the mtu

Set the received maximum size (RMS) according to the mtu size. It is
unnecessary to receive a packet which is more than the size we could
transmit. Besides, this could let the rx buffer be used effectively.

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