bonding/vlan: Remove redundant VLAN tag insertion logic

A bond may have a mixture of slave devices with and without hardware
VLAN tag insertion capability.  Therefore it always claims this
capability and performs software VLAN tag insertion if the slave does
not.

Since commit 7b9c6090, this has
also been done by dev_hard_start_xmit().  The result is that VLAN-
tagged skbs are now double-tagged when transmitted through slave
devices without hardware VLAN tag insertion!

Remove the now-redundant logic from bond_dev_queue_xmit().

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Reviewed-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>