Enable AXEN_RXCTL_START bit only when RX is ready. Otherwise,

the adapter eventually falls into "no carrier" state while it
is not running.

sys/dev/usb/if_axen.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: if_axen.c,v 1.20 2019/01/31 15:21:05 rin Exp $	*/
+/*	$NetBSD: if_axen.c,v 1.21 2019/01/31 15:22:56 rin Exp $	*/
 /*	$OpenBSD: if_axen.c,v 1.3 2013/10/21 10:10:22 yuo Exp $	*/
 
 /*
@@ -23,7 +23,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_axen.c,v 1.20 2019/01/31 15:21:05 rin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_axen.c,v 1.21 2019/01/31 15:22:56 rin Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -571,7 +571,6 @@ axen_ax88179_init(struct axen_softc *sc)
 	/* Set RX control register */
 	ctl = AXEN_RXCTL_IPE | AXEN_RXCTL_DROPCRCERR | AXEN_RXCTL_AUTOB;
 	ctl |= AXEN_RXCTL_ACPT_PHY_MCAST | AXEN_RXCTL_ACPT_ALL_MCAST;
-	ctl |= AXEN_RXCTL_START;
 	wval = htole16(ctl);
 	axen_cmd(sc, AXEN_CMD_MAC_WRITE2, 2, AXEN_MAC_RXCTL, &wval);
 
@@ -1535,9 +1534,19 @@ axen_stop(struct ifnet *ifp, int disable)
 	struct axen_softc *sc = ifp->if_softc;
 	usbd_status err;
 	int i;
+	uint16_t rxmode, wval;
 
 	axen_reset(sc);
 
+	/* Disable receiver, set RX mode */
+	axen_lock_mii(sc);
+	axen_cmd(sc, AXEN_CMD_MAC_READ2, 2, AXEN_MAC_RXCTL, &wval);
+	rxmode = le16toh(wval);
+	rxmode &= ~AXEN_RXCTL_START;
+	wval = htole16(rxmode);
+	axen_cmd(sc, AXEN_CMD_MAC_WRITE2, 2, AXEN_MAC_RXCTL, &wval);
+	axen_unlock_mii(sc);
+
 	ifp->if_timer = 0;
 	ifp->if_flags &= ~(IFF_RUNNING | IFF_OACTIVE);