kernel/802_11: Fix a panic in RUN -> AUTH -> RUN FSM transition.

When ratectl_node_init() is called and ni_rctls is already allocated,
use that pointer.

This is FreeBSD's r207323.

Pointed-out-by: Imre Vadasz <imre@vdsz.com>
Tested-by:      Markus Pfeiffer <markus.pfeiffer@morphism.de>