Reject authentication start during explicit roam requests

Reject authentication start during explicit roam requests

The roam D-Bus and ROAM control itnerface commands flip the reassociate
bit before calling wpa_supplicant_connect(). wpa_supplicant connect
eventually aborts ongoing scans (if any), which causes scan results to
be reported. Since the reassociate bit is set, this will trigger a
connection attempt based on the aborted scan's scan results and cancel
the initial connetion request. This often causes wpa_supplicant to
reassociate to the same AP it is currently associated to instead of the
explicitly requested roaming target.

Add a roam_in_progress flag to indicate that we're currently attempting
to roam via an explicitly request to a specific BSS so that we don't
initiate another connection attempt based on the possibly received scan
results from a scan that was in progress at the time the roam command
was received.

Signed-off-by: Matthew Wang <matthewmwang@chromium.org>