linux_80211: Don't dequeue lsta if not queued

This fixes an instapanic when restarting wpa_supplicant on my laptop's
iwlwifi device. After this change, iwlwifi enters a nonfunctional
state if wpa_supplicant is restarted, but "service netif restart wlan0"
is enough to get it working again.

Approved by: re (kib)

(cherry picked from commit 3689f8aeab82150da6789be87b6c2f9385810c23)
(cherry picked from commit 790dc4d825c910c8a2eda49fe9e6dd827519f0f4)