WPS: Force BSSID for WPS provisioning step connection

WPS: Force BSSID for WPS provisioning step connection

This was already done for most driver cases, but it is possible that the
BSSID/frequency is not forced if the driver reports BSS selection
capability (e.g., NL80211_ATTR_ROAM_SUPPORT). That could potentially
result in the driver ignoring the BSSID/frequency hint and associating
with another (incorrect) AP for the WPS provisioning step if that
another AP in the same ESS is more preferred (e.g., better signal
strength) by the driver and only one of the APs (the not preferred one)
is in active WPS registrar state.

While most drivers follow the BSSID hint for the initial connection to
an ESS, not doing it here for the WPS provisioning would break the
protocol. Fix this by enforcing a single BSSID/frequency to disallow the
driver from selecting an incorrect AP for the WPS provisioning
association.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>