Comment 114 for bug 1286552

Here is a solution that worked for me in Ubuntu 15.10: http://askubuntu.com/questions/754913/wifi-doesnt-reconnect-after-suspend-in-ubuntu-15-10-yet-again/754915#754915

sudo touch /lib/systemd/system-sleep/restart-networking.sh
sudo chmod +x /lib/systemd/system-sleep/restart-networking.sh
sudo nano /lib/systemd/system-sleep/restart-networking.sh

which contains:

#!/bin/sh
case "$1/$2" in
 post/*)
 echo "network-manager restart" >> /var/log/wakeup.log
 /bin/systemctl restart network-manager.service
 ;;
esac