That workaround did not work for me. However this worked:
I have still no solution but I have found a workaround:
Create a new shellscript named
hibernate.sh. Open it with gedit and
paste the following code:
gnome-screensaver-command -l dbus-send --system --print-reply \
Save it and make it executable. If you want you can create a .desktop
file for it. When you run this script it will send your pc into
hibernate-mode including the lockscreen. When you wake your pc now
networking works. When you use sleep-mode or hibernate-mode the normal
way it doesn't.
Thanks to Christopher Paul over here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1212199
Note that you'll need to restart your system once after that (if your network was out due to a suspend when you did the script). Then it works fine.
Also note this script sends your pc to suspend, not to hibernate (the name could be confusing).