Ok, it was not easy at all but I figured out how to capture packets. Since I am not extremely familiar with networking (but this new job is requesting that I am) I had difficulty with setting everything correctly. Basically after setting the right route in the VpnService.builder I got to receiving packets correctly.
So:
builder.addAddress("192.168.0.6", 24); // was wrong, you need to put an internal IP (10.0.2.0 for example)
and
builder.addRoute("0.0.0.0", 0); // needs to be this.
you don’t need to set up a DnsServer through builder.addDnsServer() to make it work. Hope this helps anyone!