[lwip-members] RFC : new file

[Jani Monoses]

Hi
what do you think of making a new file ip_frag.c and move
segmentation and reassembly code to it thus separating that from
ip.c.
I got SAR working but it still can use cleanup and optimisation and a new
file would be a better place to work on instead of cluttering the log
of ip.c. Cleaner to and in the spirit of every other free TCP stack :)
Jani.