LinuxKPI: 802.11: make sure bssid for scans (probe_req) is set

In b0f73768220e9 we added bssid[] to struct cfg80211_scan_request
likely while working on mt76 and did not need it (yet) back then.
iwlwifi started to use the field in Linux f1fec51cda70f (April 2023).
Without it set firmware crashes when trying to send probe requests
((empty) SSID also given to hw_scan).
For now always set the field to the wildcard BSSID.

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