[SOLVED] Can't use 1000Mbps speed. Stuck at 100Mbps

I decided to use a wired connection between my laptop and my RT-AC68P router (with Merlin firmware).

The result of ethtool command shows that 1000Mbps is possible with my ethernet adapter on my laptop.

prototron@ProtoMachine:~$ sudo ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: Symmetric Receive-only
Supports auto-negotiation: Yes...

[SOLVED] Can't use 1000Mbps speed. Stuck at 100Mbps