WOW ! It works :) thanks @gohan :)
I removed the voltage shifter, added an 1µF capacitor and downloaded developpement libraries.
Also, I cleaned the configuration parameters : ./configure --my-transport=nrf24 --my-gateway=ethernet
It finally works as expected (sensor, gw on rpi3, controler on debian server) and I can ditch the uno (well, I'll find him another use).
Thanks again for the wonderfull work, it's been fun :)