net: mvneta: make mvneta_eth_tool_ops static

The mvneta_eth_tool_ops is only used internally in mvneta driver, so
make it static.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>