bonding: propogate vlan_features to bonding master

Propogate the vlan_features of the slave devices to the bonding
master device, using the same logic as for regular features.

	Tested by Or Gerlitz <ogerlitz@voltaire.com>, who also removed
the debug logic from the original test patch.

Signed-off-by: Or Gerlitz <ogerlitz@voltaire.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>