Hi Simon, David,
Thanks for considering adding this static routing table implementation. Since the time I uploaded this patch there have been a few fixes and changes in the implementation that have not been updated to the patch. I will revise that with a new patch soon.
But as I gather, it seems that it would be better to get the static route table implementation as a separate standalone patch and the changes to the existing LwIP code(to invoke such a route table) as a separate one.
I will add these patches to #8680 soon.
Thanks,
Pradip