Please test: Update for intel em-7.4.2

Hi,

I have a patch [1] that updates em, emx and ig_hal to Intel's 7.4.2. 
Would be great if anyone can review
and test it!  This mainly adds support for newer I218 network cards, 
e.g. as found on the Asrock
X99 mainboard. It's working fine for me. I no one objects against, I'll 
commit.

Regards,

    Michael

[1]: 
https://github.com/mneumann/DragonFlyBSD/commit/a51574306797be948e9aeab239bba2db73bd9cea