nat: Make the code work in terms of endpoints instead of timeslot/multiplex

We are going to have more than one trunk, so all code hardcoding the
multiplex to zero must go. Avoid this kind of problem by saving the
MGCP endpoint number and comparing that.
diff --git a/openbsc/tests/bsc-nat/bsc_nat_test.c b/openbsc/tests/bsc-nat/bsc_nat_test.c
index c5234aa..b7a89c5 100644
--- a/openbsc/tests/bsc-nat/bsc_nat_test.c
+++ b/openbsc/tests/bsc-nat/bsc_nat_test.c
@@ -449,19 +449,19 @@
 		abort();
 	}
 
-	if (con.msc_timeslot != 21) {
+	if (con.msc_endp != 21) {
 		fprintf(stderr, "Timeslot should be 21.\n");
 		abort();
 	}
 
-	if (con.bsc_timeslot != 21) {
+	if (con.bsc_endp != 21) {
 		fprintf(stderr, "Assigned timeslot should have been 21.\n");
 		abort();
 	}
 	talloc_free(parsed);
 
 	bsc_mgcp_dlcx(&con);
-	if (con.bsc_timeslot != -1 || con.msc_timeslot != -1) {
+	if (con.bsc_endp != -1 || con.msc_endp != -1) {
 		fprintf(stderr, "Clearing should remove the mapping.\n");
 		abort();
 	}
@@ -483,8 +483,8 @@
 	llist_add(&con->list_entry, &nat->bsc_connections);
 
 	sccp_con = talloc_zero(con, struct sccp_connections);
-	sccp_con->msc_timeslot = 12;
-	sccp_con->bsc_timeslot = 12;
+	sccp_con->msc_endp = 12;
+	sccp_con->bsc_endp = 12;
 	sccp_con->bsc = con;
 	llist_add(&sccp_con->list_entry, &nat->sccp_connections);
 
@@ -498,13 +498,6 @@
 		abort();
 	}
 
-	sccp_con->msc_timeslot = 0;
-	sccp_con->bsc_timeslot = 0;
-	if (bsc_mgcp_find_con(nat, 1) != sccp_con) {
-		fprintf(stderr, "Didn't find the connection\n");
-		abort();
-	}
-
 	/* free everything */
 	talloc_free(nat);
 }