Unconfigured bcm43xx device can hit an assert() during wx_get_rate
queries. This is because bcm43xx calls ieee80211softmac_start late
(i.e. during open instead of probe).
bcm43xx_net_open ->
bcm43xx_init_board ->
bcm43xx_select_wireless_core ->
ieee80211softmac_start
Fix is to check that device is running before completing
ieee80211softmac_wx_get_rate.
Signed-off-by: John W. Linville <linville@tuxdriver.com>