dbus: Do not bring down primary interface when removing created AP interface

dbus: Do not bring down primary interface when removing created AP interface

If the CreateInterface command was used to create a virtual AP
interface, deleting this interface using the RemoveInterface command was
also bringing down the primary interface.

wpa_supplicant never uses hostapd style multi-BSS setup with
type=WPA_IF_AP_BSS and setup_ap=1 to if_add() when creating an AP
interface in wpa_driver_nl80211_if_add(), so it should not go through
the multi-BSS tear down procedure in wpa_driver_nl80211_if_remove(). The
virtual AP resources init and deinit are well handled in
wpa_driver_nl80211_init() and wpa_driver_nl80211_deinit().

Collapse the interface type to WPA_IF_STATION for the D-Bus interface to
skip the multi-BSS cleanup procedure. This is inline with the control
interface design. Add comments before the code to avoid confusion.

Signed-off-by: Jintao Lin <jintaolin@chromium.org>