For proxy based EAP methods, the EAP identity is constructed in
eap_proxy layer from IMSI when required. Realm information from identity
is used to do ERP eventually, hence construct the realm for proxy based
methods from IMSI in core wpa_supplicant to enable the ERP use case.
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>