bsc: Create a better error message for when RF commands are rejected

Provide an error message that makes it more clear that the command
is rejected because RF handling is not enabled in the BSC.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_ctrl.c b/openbsc/src/osmo-bsc/osmo_bsc_ctrl.c
index 40658c1..e4c6fea 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_ctrl.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_ctrl.c
@@ -395,7 +395,7 @@
 	}
 
 	if (!net->bsc_data->rf_ctrl) {
-		cmd->reply = "RF Ctrl not enabled";
+		cmd->reply = "RF Ctrl is not enabled in the BSC Configuration";
 		return CTRL_CMD_ERROR;
 	}