em(4) update (6.2.9)

[Sepherosa Ziehau]

Hi,

Following patch syncs our em(4) with Intel's 6.2.9:
http://leaf.dragonflybsd.org/~sephe/em.6.2.9.diff
Tested with 82540EM

Please test/review it.
if no objections come, it will be committed two weeks later.
Best Regards,
sephe
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