Interworking: Add sp_priority cred parameter

Interworking: Add sp_priority cred parameter

This new priority parameter can be used to specify priorities between
credentials provisioned by the same SP. cred->priority is checked first
and if it is same and the provisioning_sp parameter matches, the new
sp_priority is used to order the credentials. It should be noted that
the order of priorities is different (higher 'priority' value indicates
higher priority of the credential, while higher 'sp_priority' indicates
lower priority of the credential).

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>