net: mvpp2: set maximum packet size for 10G ports

Set maximum packet size for XLG 10G ports. Missing maximum packet size
for XLG configuration will cause kernel panic if oversized packet is
received by port.

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>