From FreeBSD (r227593, r307982):
More and more RealTek controllers started to implement EEE feature.
Vendor driver seems to load a kind of firmware for EEE with
additional PHY fixups. It is known that the EEE feature may need
ASPM support. Unfortunately there is no documentation for EEE of
the controller so enabling ASPM may cause more problems.
The Realtek vendor driver  also disables ASPM and clock request.
While here, add a define for the ECPM (Enable Clock Power Management) bit.
re0 at pci3 dev 0 function 0 "Realtek 8168" rev 0x0c: RTL8168G/8111G (0x4c00), msi, address 44:8a:5b:39:0a:25
rgephy0 at re0 phy 7: RTL8251 PHY, rev. 0
re0 at pci2 dev 0 function 0 "Realtek 8168" rev 0x03: RTL8168D/8111D (0x2800), msi, address bc:ae:c5:d6:ac:a3
rgephy0 at re0 phy 7: RTL8169S/8110S/8211 PHY, rev. 2