uether_ifdetach() never drains ue->ue_rxq — mbufs enqueued by a final RX callback that exits without flushing leak with the freed softc (live path: cdce bulk-read tr_stall skips uether_rxflush)

Summary

RX frames park on ue_rxq and deliver only on a later uether_rxflush; detach drains taskqueue/callout/miibus/sysctl but NEVER the rxq - cdce's tr_stall path (m_getcl failure or unplug between enqueue and flush) leaves frames parked when the softc is freed: repeated plug/stall/unplug cycles leak mbuf clusters (slow exhaustion DoS). IF_DRAIN-in-detach fix.