nat: Keep the state (CRCX,MDCX,DLCX) of the operation..

This will allow to have additional debug information and to
use the state inside the forwarding code.
diff --git a/openbsc/src/nat/bsc_mgcp_utils.c b/openbsc/src/nat/bsc_mgcp_utils.c
index 17c4bbf..6644c5e 100644
--- a/openbsc/src/nat/bsc_mgcp_utils.c
+++ b/openbsc/src/nat/bsc_mgcp_utils.c
@@ -94,6 +94,7 @@
 		nat->bsc_endpoints[i].transaction_id = NULL;
 	}
 
+	nat->bsc_endpoints[i].transaction_state = 0;
 	nat->bsc_endpoints[i].bsc = NULL;
 }
 
@@ -202,6 +203,7 @@
 		     endpoint, bsc_endp->transaction_id);
 		talloc_free(bsc_endp->transaction_id);
 		bsc_endp->transaction_id = NULL;
+		bsc_endp->transaction_state = 0;
 	}
 	bsc_endp->bsc = NULL;
 
@@ -237,6 +239,7 @@
 
 
 	bsc_endp->transaction_id = talloc_strdup(nat, transaction_id);
+	bsc_endp->transaction_state = state;
 	bsc_endp->bsc = sccp->bsc;
 
 	/* we need to update some bits */
@@ -325,6 +328,7 @@
 	/* free some stuff */
 	talloc_free(bsc_endp->transaction_id);
 	bsc_endp->transaction_id = NULL;
+	bsc_endp->transaction_state = 0;
 
 	/*
 	 * rewrite the information. In case the endpoint was deleted