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.

releng/13.2 candidate.

Reviewed by: bz
MFC after: 3 days