Hello, @Atkinson
Thanks for the post.
1. LWIP is a software stack, usually the code is running with host, it is suggested integrating it to your M core application, regardless the network traffic to sja1110 or to PFE directly.
2. Currently there is no directly IPv6 samples existed, there is a LWIP bare metal example, which is using the GMAC interface, you may firstly use it for your reference.
It is by default using the IPv4, and you will need to change the code to try with IPv6, there is not public document from NXP for describing it, I suggest directly reference the introduction from LWIP, for example: https://www.nongnu.org/lwip/2_1_x/group__lwip__opts__ipv6.html
BR
Chenyin