net/sched: act_police: disallow 'goto chain' on fallback control action

net/sched: act_police: disallow 'goto chain' on fallback control action

in the following command:

 # tc action add action police rate <r> burst <b> conform-exceed <c1>/<c2>

'goto chain x' is allowed only for c1: setting it for c2 makes the kernel
crash with NULL pointer dereference, since TC core doesn't initialize the
chain handle.

Signed-off-by: Davide Caratti <[email protected]>
Acked-by: Cong Wang <[email protected]>
Acked-by: Jiri Pirko <[email protected]>
Signed-off-by: David S. Miller <[email protected]>