stat-util: rename files_same() → inode_same()

Let's be more accurate about what this function does: it checks whether
the underlying reported inode is the same. Internally, this already uses
a better named stat_inode_same() call, hence let's similarly name the
wrapping function following the same logic.

Similar for files_same_at() and path_equal_or_same_files().

No code changes, just some renaming.

src/basic/namespace-util.c

@@ -109,7 +109,7 @@ int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int userns_fd, int
                 /* Can't setns to your own userns, since then you could escalate from non-root to root in
                  * your own namespace, so check if namespaces are equal before attempting to enter. */
 
-                r = files_same(FORMAT_PROC_FD_PATH(userns_fd), "/proc/self/ns/user", 0);
+                r = inode_same(FORMAT_PROC_FD_PATH(userns_fd), "/proc/self/ns/user", 0);
                 if (r < 0)
                         return r;
                 if (r)