EAP-AKA/AKA' peer: Allow external USIM processing to be used

EAP-AKA/AKA' peer: Allow external USIM processing to be used

This allows the new external_sim=1 case to be used to perform UMTS
authentication step in EAP-AKA/AKA' peer process. Following control
interface event is used to request the operation:

CTRL-REQ-SIM-<network id>:UMTS-AUTH:<RAND>:<AUTN> needed for SSID <SSID>

Response from external processing is returned with
CTRL-RSP-SIM-<network id> UMTS-AUTH:<IK>:<CK>:<RES>
or
CTRL-RSP-SIM-<network id> UMTS-AUTS:<AUTS>

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