Debian stretch failed to load firmware rtl_nic/rtl8168g-3.fw (-2)
After one hour of searching on different resources i ends up by solving the problem which was caused by a missing of firmware-realtek the realtek driver .
The missing of this firmware can throw different errors prefixed by rtl_nic/ to solve this simply add the official repository Debian firmware-realtek to your /etc/apt/sources.list and make sure you are selecting the right destro
your source.list should look like this:
#realtek firmware
deb http://ftp.de.debian.org/debian stretch main non-free
deb-src http://ftp.de.debian.org/debian stretch main non-free
After that install realtek firmware
sudo apt-get update
sudo apt-get install firmware-realtek