ctrl: Remember last 'rf_locked' control command

This stores the last SET rf_locked control command along with a
timestamp. The 'show network' vty command is extended to show
this information.

Ticket: OW#659
diff --git a/openbsc/src/libbsc/bsc_rf_ctrl.c b/openbsc/src/libbsc/bsc_rf_ctrl.c
index bd36e18..9eb85e5 100644
--- a/openbsc/src/libbsc/bsc_rf_ctrl.c
+++ b/openbsc/src/libbsc/bsc_rf_ctrl.c
@@ -504,6 +504,7 @@
 	rf->gsm_network = net;
 	rf->policy = S_RF_ON;
 	rf->last_state_command = "";
+	rf->last_rf_lock_ctrl_command = talloc_strdup(rf, "");
 
 	/* check the rf state */
 	rf->rf_check.data = rf;