net: ethernet: mediatek: add ethtool functions to configure RX flows of HW LRO

The codes add ethtool functions to set RX flows for HW LRO. Because the
HW LRO hardware can only recognize the destination IP of TCP/IP RX flows,
the ethtool command to add HW LRO flow is as below:
ethtool -N [devname] flow-type tcp4 dst-ip [ip_addr] loc [0~1]

Otherwise, cause the hardware can set total four destination IPs, each
GMAC (GMAC1/GMAC2) can set two IPs separately at most.

Signed-off-by: Nelson Chang <nelson.chang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>