bsc: Create a osmo_bsc_data and embed osmo_msc_data

We want to have multiple MSCs but we also have some data
that is only present on a per BSC basis. Right now the
MSC data is not allocated with talloc, so we have some
change in the talloc contexts.
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index 8c39b3a..ce493d7 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -197,9 +197,9 @@
 	dump_pchan_load_vty(vty, "    ", &pl);
 
 	/* show rf */
-	if (net->msc_data && net->msc_data->rf_ctrl)
+	if (net->bsc_data && net->bsc_data->rf_ctrl)
 		vty_out(vty, "  Last RF Command: %s%s",
-			net->msc_data->rf_ctrl->last_state_command,
+			net->bsc_data->rf_ctrl->last_state_command,
 			VTY_NEWLINE);
 }