EAP-SIM/AKA server: Allow method specific identity exchange to be skipped

EAP-SIM/AKA server: Allow method specific identity exchange to be skipped

While the EAP-SIM/AKA RFCs recommend against doing this, some deployed
authentication servers use the identity from the EAP-Response/Identity
directly without using an EAP method specific indication (AT_IDENTITY).
Having a capability to configure hostapd EAP server to behave in this
manner helps in increasing testing coverage for the EAP peer
implementation.

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