Raspberry: No Wifi after upgrade (wpa_supplicant, libnl-3.so.200)

Running OSMC successfully for years on Raspi 2 with touchscreen and hifiberry.
After the last upgrade and reboot, wifi did not come up and therefore OSMC fails to start, showing a white frownie symbol on black background.

connmanctl shows no wifi technology.

Entering “wpa_supplicant” in a root shell gives:
wpa_supplicant: error while loading shared libraries: libnl-3.so.200: Wrong ELF class: ELFCLASS64

uname -a gives
Linux osmc-pi 4.14.78-4-osmc #1 SMP PREEMPT Wed Dec 12 17:58:11 UTC 2018 arm7l GNU/Linux

So it appears that the lib has to be - wrongly - replaced with a 64 bit binary on my 32 bit system. How can I find and put the correct library?

Could it be you added a wrong package repository? Check your sources.list.
Also if you can create a internet connection via wireless upload logs with grab-logs -A

I did not mess with the repositories, currently it is:
deb http://ftp.debian.org/debian stretch main contrib non-free
deb Index of /debian stretch-updates main contrib non-free
deb http://security.debian.org/ stretch/updates main contrib non-free
deb http://apt.osmc.tv stretch main

(Don’t have an internet connection right now, sorry. grab-logs -A just says “Killed” after some time.)

You can see the ELF header data with:

readelf -h /lib/arm-linux-gnueabihf/libnl-3.so.200

If at all possible, connect the Pi by cable to a router/switch and try to reinstall the affected library:

sudo apt-get update
sudo apt-get install --reinstall libnl-3-200

(NB The IP address will probably be different on cable.)