bsc: Call the RF Control interface ctrl all the way

We had the rf_ctrl_name and the rf_ctl pointer, make both use
the word ctrl.
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index a290693..54d7c6e 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -189,9 +189,9 @@
 	dump_pchan_load_vty(vty, "    ", &pl);
 
 	/* show rf */
-	if (net->msc_data && net->msc_data->rf_ctl)
+	if (net->msc_data && net->msc_data->rf_ctrl)
 		vty_out(vty, "  Last RF Command: %s%s",
-			net->msc_data->rf_ctl->last_state_command,
+			net->msc_data->rf_ctrl->last_state_command,
 			VTY_NEWLINE);
 }