DPP: Allow Relay connections to Controllers to be added and removed

DPP: Allow Relay connections to Controllers to be added and removed

The new control interface commands "DPP_RELAY_ADD_CONTROLLER <IP addr>
<PK hash>" and "DPP_RELAY_REMOVE_CONTROLLER <IP addr>" can now be used
to dynamically add and remove connections to Controllers for the cases
where the connection is initialized through a DPP Public Action frame
(i.e., Controller as the Responder).

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>