Providing lwIP's HTTPd as RIOT module

Hi @miri64 , thanks.

I tried this change but it didn’t work.

I can’t figure out where the “multiple definition” errors are coming from. I’m researching on the one hand, but I would be very pleased if I could get support from you as well.

EDIT: Previously I said

but this is not true, fs.c file has #include HTTPD_FSDATA_FILE