Hi Simon,
Thanks for the reply.
Yes, you are correct. I did't phrase the problem well.
The reason I wanted to do this is that I have integrated lwip stack in my virtual simulation platform, and I am trying to do some quick hacking to extract profiling data of executing lwip on raspberry pi, that's the reason I executed lwip in the user space on top of linux. So for this purpose, instead of actually merging lwip into kernel, do you think there is some simpler way to do the packet sniffers? Basically I need to sniff the packets from the on board wireless interface (wlan0), and it seems that bridging is not supported by the wlan driver...