From what I have deduced through email exchanges with Chelsio support, they're not really big fans of supporting Debian as priority, they are hell bent on sticking with Red Hat, lo and behold RHV comes with all the offloading features enabled. The growth of Proxmox in enterprise is getting noticed by hardware manufacturers and hopefully in good time Debian will gain better support from manufacturer driver developers. Fingers crossed.
For now it is going to be just us part-time 'hackers' trying to get things to work.
Yes, I will take your advice on board (though I may need some assistance if I hit a wall), and do the patch that way, it does indeed make sense.
If my endeavours are successful my effort can at least be easily portable to other Proxmox users with Chelsio hardware.
Fresh off the press - Well good news is that I have actually JUST NOW got the modules built successfully!!! Now for a late evening of ample testing!