rtnetlink & bonding: change args got get_tx_queues

Change get_tx_queues, drop unsused arg/return value real_tx_queues,
and use return by value (with error) rather than call by reference.

Probably bonding should just change to LLTX and the whole get_tx_queues
API could disappear!

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>