[Serusers] Missed Call Return

[Andreas Granig]

I wrote:
> So you're right, it would be nicer to call avp_db_delete before 
> avp_db_store in failure_route.

So finally the corrected failure-route looks like this (needs an 
additional DB query though):

failure_route[2] {
     if(t_check_status("480|486") && method == "INVITE") {
         avp_write("$from", "$callback");
         revert_uri();
         avp_db_delete("$ruri", "$callback/callback");
         avp_db_store("$ruri", "$callback/callback");
         avp_delete("$callback");
     }
}

Andy