net80211: introduce two extra ieee80211_notify_scan_done()

We have multiple problems with scanning currently, one being that
an initial scan restarts itself and we are unable to start another
scan. wpa_supplicant in that case never shows scan results.
Starting wpa_cli you may see: <3>CTRL-EVENT-SCAN-FAILED ret=-1 retry=1
messages.
Add two extra calls to ieee80211_notify_scan_done() at the end of scans
(before possible restarts). That will get wpa_supplicant to get
scan results and possibly start associating to a BSSID and get us out
of scan. This is kind-of a bandaid but on short notice may help to
improve the situation for some.

Based on analysis by: enweiwu
Submitted by: enweiwu (initial version)
Sponsored by: The FreeBSD Foundation
Tested by: cy, (others I cannot find email/PR for anymore)
Reviewed by: cy
Differential Revision: https://reviews.freebsd.org/D38661

(cherry picked from commit 3f382eb23b9fee75d05276a44feb5351d956238e)