P2P: Fix memory leak with driver-based P2P management
If the P2P management operations are handled within the driver, the
P2P service entries were not freed when terminating wpa_supplicant.
Fix this by calling wpas_p2p_service_flush() even if the P2P module
within wpa_supplicant has not been initialized.
Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>