net: bonding: Inherit MPLS features from slave devices

When setting the bonding interface net device features,
the kernel code doesn't address the slaves' MPLS features
and doesn't inherit them.

Therefore, HW offloads that enhance performance such as
checksumming and TSO are disabled for MPLS tagged traffic
flowing via the bonding interface.

The patch add the inheritance of the MPLS features from the
slave devices with a similar logic to setting the bonding device's
VLAN and encapsulation features.

CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>