After updating the driver in the 13th release. Regression was introduced.
12.2 RELEASE and 12-STABLE allow you to set the interface to PROMISC mode if VTNET_FLAG_CTRL_RX is not advertised by the hypervisor.
But, 13-RELEASE allow this only if VTNET_FLAG_CTRL_RX is advertised.
For example, bhyve(8) doesn't support VTNET_FLAG_CTRL_RX.
Technically, if the hypervisor doesn't support the VTNET_FLAG_CTRL_RX, then the interface is always in PROMISC mode.
I see no reason to prohibit switching the interface to PROMISC mode if VTNET_FLAG_CTRL_RX is not supported by the hypervisor.
PR: 254343 and PR: 255054
This changes restore 12-STABLE behavior https://github.com/freebsd/freebsd-src/blob/stable/12/sys/dev/virtio/network/if_vtnet.c#L1103:
if ((ifp->if_flags ^ sc->vtnet_if_flags) &
(IFF_PROMISC | IFF_ALLMULTI)) {
if (sc->vtnet_flags & VTNET_FLAG_CTRL_RX)
vtnet_rx_filter(sc);
else {
ifp->if_flags |= IFF_PROMISC;
if ((ifp->if_flags ^ sc->vtnet_if_flags)
& IFF_ALLMULTI)
error = ENOTSUP;
}
}