Okay so here’s an interesting tidbit:
If I reboot the laptop, the link LEDs actually come back up during the POST boot, before the kernel loads. Then when the Linux kernel runs, they turn off and then back on, steadily, until … something runs and then they turn back off.
So something is breaking this during boot, because in the BIOS, it just works! Fascinating!
I bet this is a problem with powertop. When I run powertop, there is an entry like this in the Tunables tab:
Good Autosuspend for USB device USB 10/100/1G/2.5G LAN [Realtek]
Hitting space bar here magically fixes the ethernet card, woohoo!
Or, if you will, this magic command whould turn the card back on:
echo 'on' > '/sys/bus/usb/devices/4-2/power/control';
to revert:
echo 'auto' > '/sys/bus/usb/devices/4-2/power/control';
… interestingly, even in auto mode, the card still works. So maybe there’s something in the powertop setup code that breaks this…
I’ll notify support, but I think this might be a fix for you, @samdas @Cameron_Abma 
Well that is certainly much better!
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 1.09 GBytes 937 Mbits/sec 238 sender
[ 5] 0.00-10.00 sec 1.09 GBytes 934 Mbits/sec receiver
whoohoo!