bonding: implement get_tx_queues rtnk_link_op

If bonding device is created via rtnl, it is created with default number
of rx/tx queues. This patch implements callback in bonding so the
correct value (previously specified by bonding module param) is used.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>