iflib: don't update the admin status in if_media_status

[gallatin]

Summary

When _task_fn_admin() is active, it will regularly call IFDI_UPDATE_ADMIN_STATUS(). So there is no need to do it in iflib_media_status. This can be fairly expensive on some drivers (long DELAY bussywait loops waiting for a NIC command), and there is no need to pause a userspace app in this DELAY() if it is happening asynchronously anyway.

Note the logic to detect if _task_fn_admin() is regularly calling IFDI_UPDATE_ADMIN_STATUS() was copied from that function.

[erj]

I like the idea.

[kbowling]

Confirmed safe for all in tree drivers. Maybe worth a man page update in iflibdd(9).