To build your OpenWRT-Image for a TP-Link TL-WR841ND V14:
Minimal configuration without comfort, luci and without ipv6. Realy minimal! But cli is working. To use wifi and the switch with routing capabilities, DHCP and firewall it works.
To install use tftp-image (3.9MB) AND afterwards do a sysupgrade (3.6MB). In other case overlay filesystem is not working and configuration will be lost after restart.
PS. : Tried to activate openvpn-nossl but no success. Any ideas?