RSN: Update preauth scan results only based on new scan results

RSN: Update preauth scan results only based on new scan results

The fast-connect optimization to skip a new scan did not update how the
RSN preauthentication callback is used. There is no point in trying to
add preauthentication candidates from cases where scan was skipped, so
skip this call, too, in such cases.

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