NetworkManager: Disable Sending Hostname to DHCP Server

Edit /etc/NetworkManager/NetworkManager.conf file to contain the following default settings for new connections:
[connection]
ipv4.dhcp-send-hostname=false
ipv6.dhcp-send-hostname=false
Disable sending hostname to DHCP server for already existing connections:
nmcli -t -f uuid connection | while read uuid; do
 nmcli connection modify $uuid \
 ipv4.dhcp-send-hostname false \
 ipv6.dhcp-send-hostname false
done
Restart NetworkManager to apply the settings:
systemctl restart NetworkManager