bsc_api: Make paging/silent call work with the subscriber_connection

Do not use the lchan for the paging but operate on the
subscriber_connection, change the signals too to not carry
the lchan but the subscriber connection... the silent call
and vty code still assume there is a lchan inside the
subscriber connection.
diff --git a/openbsc/src/vty_interface_layer3.c b/openbsc/src/vty_interface_layer3.c
index 7c32c05..2a31df6 100644
--- a/openbsc/src/vty_interface_layer3.c
+++ b/openbsc/src/vty_interface_layer3.c
@@ -513,7 +513,7 @@
 	switch (signal) {
 	case S_SCALL_SUCCESS:
 		vty_out(vty, "%% silent call on ARFCN %u timeslot %u%s",
-			sigdata->lchan->ts->trx->arfcn, sigdata->lchan->ts->nr,
+			sigdata->conn->lchan->ts->trx->arfcn, sigdata->conn->lchan->ts->nr,
 			VTY_NEWLINE);
 		break;
 	case S_SCALL_EXPIRED: