make 'sta' argument of 'query_sta_metrics' mandatory

src/cntlr_commands.c

@@ -131,7 +131,7 @@ DEFINE_ATTR(query_sta_metrics) = {
 		.help = "AL-address of Agent to which STA Metrics Query is to be sent",
 	},
 	[STA_METRICS_ATTR_STA] = {
-		.optional = 1,
+		.optional = 0,
 		.pol = {
 			.name = "sta",
 			.type = BLOBMSG_TYPE_STRING,