Fix Comment of ETH_P_802_3_MIN

The description of ETH_P_802_3_MIN is misleading.
The value of EthernetType in Ethernet II frame is more than 0x0600,
the value of Length in 802.3 frame is less than 0x0600.

Signed-off-by: Xiayu Zhang <Xiayu.Zhang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>