pkg/libcoap: fix build AND tests: add one to ensure it does not break in the future

You add whitespace changes to this patch file, but the Commit message still says: "Remove two example programs in root" which is weird, IMHO. I provided my repository, because

a) the changes are more current (and we could use this PR to finally add them)
b) you would have an actual repository to work on and rework your changes from there.