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/rrlp.c b/openbsc/src/rrlp.c
index b5c7daf..465d206 100644
--- a/openbsc/src/rrlp.c
+++ b/openbsc/src/rrlp.c
@@ -91,7 +91,7 @@
 	switch (signal) {
 	case S_PAGING_SUCCEEDED:
 		/* A subscriber has attached. */
-		send_rrlp_req(&psig_data->lchan->conn);
+		send_rrlp_req(psig_data->conn);
 		break;
 	case S_PAGING_EXPIRED:
 		break;