cxgb3: fix crash due to manipulating queues before registration

Along the same lines as "cxgb4: fix crash due to manipulating queues
before registration" (8f6d9f40), before
commit "net: allocate tx queues in register_netdevice"
netif_tx_stop_all_queues and related functions could be used between
device allocation and registration but now only after registration.
cxgb4 has such a call before registration and crashes now.  Move it
after register_netdev.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: eric.dumazet@gmail.com
Cc: sonnyrao@us.ibm.com
Cc: Divy Le Ray <divy@chelsio.com>
Cc: Dimitris Michailidis <dm@chelsio.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Tested-by: Nishanth Aravamudan <nacc@us.ibm.com>
Acked-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>