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/include/openbsc/osmo_bsc_rf.h b/openbsc/include/openbsc/osmo_bsc_rf.h
index a67e1bd..19ccd08 100644
--- a/openbsc/include/openbsc/osmo_bsc_rf.h
+++ b/openbsc/include/openbsc/osmo_bsc_rf.h
@@ -33,6 +33,8 @@
 
 	const char *last_state_command;
 
+	char *last_rf_lock_ctrl_command;
+
 	/* delay the command */
 	char last_request;
 	struct osmo_timer_list delay_cmd;