style: cppcheck — const-correctness in file_send_special and test_chunk

file_send_special now takes const File*; test_chunk declares the deserialized
Chunk* const.  cppcheck (--error-exitcode=1) now exits clean; clang-format
clean; unit 29/29.

src/shared/file_send.c

@@ -22,7 +22,7 @@
  * frame: the destination path, the metadata frame (whose mode's S_IFMT bits
  * carry the node kind) and the device rdev major/minor.  The receiver validates
  * the kind and rdev and recreates the node (privilege-gating the mknod). */
-bool file_send_special(File* file, int file_descriptor, bool use_metadata) {
+bool file_send_special(const File* file, int file_descriptor, bool use_metadata) {
   if (!file || !file_wire_path(file))
     return false;
   if (!send_status(file_descriptor, STATUS_SPECIAL))

src/shared/file_send.h

@@ -6,7 +6,7 @@
 
 /* Client-side file send path. */
 
-bool file_send_special(File* file, int file_descriptor, bool use_metadata);
+bool file_send_special(const File* file, int file_descriptor, bool use_metadata);
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path);
 bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,