DF-4930 sink-run serial-console evidence (captured from dfbsd-qemu/boot.log
immediately after the run):

  uafsink: loaded; sysctl hw.uafsink_fire=1 to panic
  uafsink: ifmedia_init (empty list)
  uafsink: list walk done, media=0x0; calling ifmedia_set (mii.c:244)
  ifmedia_set: no match for 0x0/0xffffffff
  panic: ifmedia_set
  cpuid = 1
  Trace beginning at frame 0xfffff80117ca3758
  ifmedia_set() at ifmedia_set+0x53 0xffffffff807432b3
  ifmedia_set() at ifmedia_set+0x53 0xffffffff807432b3
  uafsink_fire() at uafsink_fire+0x8e 0xffffffff8260110e
  sysctl_root.isra.5() at sysctl_root+0x166 0xffffffff80683d06
  userland_sysctl() at userland_sysctl+0x111 0xffffffff806840a1
  sys___sysctl() at sys___sysctl+0x74 0xffffffff80684204
  Debugger("panic")

  CPU1 stopping CPUs: 0x0000003d
   stopped
  Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
  db>

This executes the exact kernel-side tail of the atphy no-media attach chain:
atphy.c:140-144 ("no media present", mii_phy_add_media skipped) ->
atphy.c:149 MIIBUS_MEDIAINIT -> miibus_mediainit (mii.c:229-246, empty list,
media stays 0) -> ifmedia_set (sys/net/if_media.c) -> panic("ifmedia_set").

DragonFly-specific: FreeBSD's ifmedia_set prints a warning and RETURNS on a
no-match; DragonFly's panics.