This is a regression. The tg3 driver works fine on 4.4.203 on Mac Mini 6,1 and 6,2 computers, but will silently drop all packets after a tiny load on all newer kernel versions.

To reproduce:
 1) use a Mac Mini 6,1 or 6,2 or computer with the same network chip.
 2) ssh root@macmini dd if=/dev/urandom | dd of=/dev/null
 3) watch the bandwidh on the macmini. It will drop to 0b/s after a few moments

Mac Mini 6,2
  4.4.203 is not affected (12 hours, high cpu load, over 800GB transferred without error)
  4.9.203 is affected (eth0 timeout after only 6.3GB of transfer, no messages in dmesg)
  4.14.156 is affected (eth0 timeout in seconds after only 1.5GB of transfer, no messages in dmesg)
  5.3.11 is affected (eth0 timeout after only 6.3GB of transfer, no messages in dmesg)
  5.4 is affected (eth0 timeout after only 10GB of transfer, no messages in dmesg)

Changing tx rx sg and tso with ethtool does not help.