net: ethernet: Remove repeating expression

Identify issues that arise by using the tests/doublebitand.cocci
semantic patch. Need to remove duplicate expression in if statement.

Signed-off-by: Wang Ming <machel@vivo.com>
Reviewed-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>