Ethtool variable for permanently applying Ethtool settings
Changes made with Ethtool are reverted by default after a reboot. To apply custom settings every time the system boots, edit the configuration file for the interface:
vi /etc/sysconfig/network-scripts/ifcfg-enp0s3
Add the desired values as a new line at the end of the file using this syntax:
ETHTOOL_OPTS="speed [100|1000|10000] duplex [half|full] autoneg [on|off]"
For example:
ETHTOOL_OPTS="speed 1000 duplex full autoneg on"
Save the file and exit.
From that point on, the change will be applied after every reboot and will remain active until the file is changed again.
Source: How to Change Speed/Duplex of Ethernet Card Linux {Ethtool Commands}