cnic: Fix rtnl deadlock

When cnic_stop_hw() -> cnic_cm_stop_bnx2x_hw() is called under rtnl_lock()
from NETDEV_DOWN event, it waits for cnic_delete_task() to complete.
It will deadlock when cnic_delete_task() takes rtnl_lock() before
calling cnic_ulp_stop_one().

We fix it by removing the rtnl_lock() in cnic_delete_task().
cnic_ulp_stop_one() has mutex and atomic bit ops to prevent important
operations from being done more than once, so it is not necessary to take
rtnl_lock().

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>