net: vlan: Inherit MPLS features from parent device

During the creation of the VLAN interface net device,
the various device features and offloads are being set based
on the parent device's features.
The code initiates the basic, vlan and encapsulation features
but doesn't address the MPLS features set and they remain blank.
As a result, all device offloads that have significant performance
effect are disabled for MPLS traffic going via this VLAN device such
as checksumming and TSO.

This patch makes sure that MPLS features are also set for the
VLAN device based on the parent which will allow HW offloads of
checksumming and TSO to be performed on MPLS tagged packets.

Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>