Using XDP in docker swarm to track outgoing traffic

Hi everyone,
I am trying to use XDP to track outgoing traffic from docker containers 
deployed using docker swarm and running in a network using the driver 
overlay. I am using a simple xdp program based on [1], and I run this 
program on the network namespace of the container using nsenter and 
attach it to its eth0.
However, I am only able to detect the incoming packets and not the 
outgoing ones. When running tcpdump on the container network namespace I 
can see both incoming and outgoing packets. So I am a bit confused as to 
why XDP would not detect the outgoing ones.
Does anyone know why the reason for this or a general idea as to why 
this might happen?

[1]https://github.com/iovisor/bcc/blob/master/examples/networking/xdp/xdp_drop_count.py

Best Regards,
Sebastião Amaro