macsec_linux: Exit early when missing macsec kernel module

Using driver macsec_linux makes no sense without macsec kernel module
loaded.

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>

src/drivers/driver_macsec_linux.c

@@ -234,10 +234,44 @@ static void macsec_drv_wpa_deinit(void *priv)
 }
 
 
+static int macsec_check_macsec(void)
+{
+	struct nl_sock *sk;
+	int err = -1;
+
+	sk = nl_socket_alloc();
+	if (!sk) {
+		wpa_printf(MSG_ERROR, DRV_PREFIX "failed to alloc genl socket");
+		return -1;
+	}
+
+	if (genl_connect(sk) < 0) {
+		wpa_printf(MSG_ERROR,
+			   DRV_PREFIX "connection to genl socket failed");
+		goto out_free;
+	}
+
+	if (genl_ctrl_resolve(sk, "macsec") < 0) {
+		wpa_printf(MSG_ERROR,
+			   DRV_PREFIX "genl resolve failed - macsec kernel module not present?");
+		goto out_free;
+	}
+
+	err = 0;
+
+out_free:
+	nl_socket_free(sk);
+	return err;
+}
+
+
 static void * macsec_drv_wpa_init(void *ctx, const char *ifname)
 {
 	struct macsec_drv_data *drv;
 
+	if (macsec_check_macsec() < 0)
+		return NULL;
+
 	drv = os_zalloc(sizeof(*drv));
 	if (!drv)
 		return NULL;