I did a "lspci", and there are two mentions of ethernet controllers...
02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 03)
03:06.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet (rev 10)
I assume the first one refers to my second (working) NIC, but it's not PCIe (it's normal PCI), so I am confused there.
Now the second one - is that refering to the onboard NIC? But then I think that the onboard NIC isn't PCI, so how can it be? I just don't know.