P2P: Fix disconnect event not to increase idle timeout

P2P: Fix disconnect event not to increase idle timeout

When P2P client is processing a disconnection event, make sure the P2P
idle timeout does not get increased, i.e., set a new timeout only if no
timeout is in use. wpa_state changes between DISCONNECTED and SCANNING
can generate multiple calls to wpas_p2p_notif_disconnect() and
previously this was enough to force the idle timeout never hit in
practice when in P2P client role.

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