Sounds like issues I've seen that that I recall "solving" by simply
disabling NetworkManager. Iirc, there is a driver for some Intel
interfaces that is known to sometimes take too long to do some
initialization step that causes NetworkManager to keep resetting the
port (or something like that
Upgraded one of our boxes from 7.6 to 7.9 and no network connections.
Looked at Ethernet connection and no lights. Unpluged the cable and
plugged it back in and you could see lights and then they went off.
After tripple checking everything I could think of we rebooted to 7.6
and presto it all
