net: mvneta: enable features before registering the driver

It seems that the reason why the dev features were ignored was because
they were enabled after registeration.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>