RADIUS server: Accept ERP keyName-NAI as user identity

RADIUS server: Accept ERP keyName-NAI as user identity

Previously the EAP user database had to include a wildcard entry for ERP
to work since the keyName-NAI as User-Name in Access-Request would not
be recognized without such wildcard entry (that could point to any EAP
method). This is not ideal, so add a separate check to allow any stored
ERP keyName-NAI to be used for ERP without any requirement for the EAP
user database to contain a matching entry.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>