Do the auth check in bsc_nat_filter_sccp_cr, remove the cause from
the signature again. For the bsc_nat_filter_dt restructure the flow
but leave the auth inside the id response message.
Return 1 when the IMSI has been extracted as indicator for running
the auth check. 1 has not been used before and is safe to be used
as this indicator.
In preparation for another kind of black-list allow the filter code
to decide how the connection should be rejected. Introduce a new struct
that will carry the reject causes for certain operations.
Holger Hans Peter Freyther