(baseline run, DFBATCH kernel, captured from serial console)
DFB-uether[mii]: fabricating mii_phy_probe-failure state
DFB-uether: if_link = {0, 0} (if_attach never ran), calling verbatim uether_ifdetach()
DFB-uether: expect if_detach() TAILQ_REMOVE through tqe_prev == NULL -> kernel panic now
fault virtual address	= 0x0
Stopped at      if_down_dispatch+0x66:  movq    (%rax),%r13
[ether_ifdetach() -> if_down() on the never-attached ifnet: first NULL
 deref lands in if_down_dispatch before the predicted TAILQ_REMOVE;
 same class -- detach machinery on a never-if_attach()ed ifnet]