Do not use results from externally requested scan for network selection

Do not use results from externally requested scan for network selection

It may not always be desirable to trigger reassociation or network
change based on scan results from externally to wpa_supplicant trigger
scan operations. Skip network selection and roaming determination if the
received scan result is known to be triggered by something external to
wpa_supplicant. The control interface SCAN command can be used to
request wpa_supplicant to determine the best network.

Signed-hostap: Jouni Malinen <j@w1.fi>