rtnetlink: ops->get_tx_queue() cannot take a const 'tb'.

net/core/rtnetlink.c: In function ‘rtnl_create_link’:
net/core/rtnetlink.c:1645:3: warning: passing argument 2 of ‘ops->get_tx_queues’ from incompatible pointer type [enabled by default]
net/core/rtnetlink.c:1645:3: note: expected ‘const struct nlattr **’ but argument is of type ‘struct nlattr **’

Signed-off-by: David S. Miller <davem@davemloft.net>