This worked perfect for me. I had to install iw and iwconfig through the unofficial openelec repo but was able to get this working by creating the autostart.sh and pointing to the location of my iwconfig ( /storage/.kodi/addons/http://tools.iw/bin/iw wlan0 set power_save off )
Hello,
on LibreELEC (official) Version: 7.0.2 (on RPI3)
first install -> Libreelec Addons/Program Addons/Network Toolsreboot
logon via ssh and test -> iwconfig
wlan0 shows up like -> Power Management:on
then -> nano /storage/.config/autostart.sh
add -> iw wlan0 set power_save off
-> save and exit
-> rebootlogon via ssh and test -> iwconfig
wlan0 shows up like -> Power Management:off
...maybe the solution