VTN Coordinator cannot be built on Fedora 25.

I tries to build VTN Coordinator on Fedora 25, but it failed due to the following compiler warning.

rmpath.c: In function 'dir_cleanup':
rmpath.c:262:2: error: 'readdir_r' is deprecated [-Werror=deprecated-declarations]
while ((err = readdir_r(dirp, buf, &dp)) == 0) {
^~~~~
In file included from rmpath.c:17:0:
/usr/include/dirent.h:183:12: note: declared here
extern int readdir_r (DIR *__restrict __dirp,

readdir_r() is marked as deprecated as of glibc-2.24. But I think we should ignore that warning because no suitable substitute is provided.