if_em(4) carrier loss event not recognized with i217; while 82574 does recognize

Thu May 10 19:17:05 UTC 2018

 Hello,

if I pull the TP connection from my i217 Clarkville, HEAD still reports
media
1000Base-T status "active".

Doing the same with the other if_em(4) NIC in that box, a hartwell,
82574LM, the status correctly changes to "no carrier".

This is not iflib related, since it's reproducable with FreeBSD
11-stable (some months old).

Shall I file a PR?

-harry