EAP-SIM DB: Store permanent username as string in SQLite DB

EAP-SIM DB: Store permanent username as string in SQLite DB

Store permanent username (i.e., including prefix character) instead of
IMSI in the SQLite DB. Convert the string to a string since the EAP-AKA
prefix can start with zero. This cleans up the field names since the
value was already with the prefix included instead of just IMSI. In
addition, this explicitly removes some theoretical cases where the
different identity types could have been mixed.

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