(see run.harness.log for the decisive run; guest has no emx hardware --
 kldload if_emx succeeds, module loads, no emx interface appears:
   $ kldload if_emx && echo KLDLOAD_OK; kldstat | grep emx; ifconfig -l
   KLDLOAD_OK
     4    1 0xffffffff82600000    65000 if_emx.ko
   vtnet0 lo0
 device-side descriptor injection documented in README.md)