Improve static and const correctness.

- Any non-externally-visible declarations should be `static`.
- Casting away the `const` qualifier from pointers-to-const is
  dangerous. All but one instance of this are now correct. The one
  instance where we can't keep `const` is one where toxav code actually
  writes to a chunk of memory marked as `const`. This code also assumes
  4 byte alignment of data packets. I don't know whether that is a valid
  assumption, but it's likely unportable, and *not* obviously correct.
- Replaced empty parameter lists with `(void)` to avoid passing
  parameters to it. Empty parameter lists are old style declarations for
  unknown number and type of arguments.
- Commented out (as `#if DHT_HARDENING` block) the hardening code that
  was never executed.
- Minor style fix: don't use `default` in enum-switches unless the number
  of enumerators in the default case is very large. In this case, it was
  2, so we want to list them both explicitly to be warned about missing
  one if we add one in the future.
- Removed the only two function declarations from nTox.h and put them
  into nTox.c. They are not used outside and nTox is not a library.

1 files changed, 2 insertions, 2 deletions

diff --git a/toxcore/util.c b/toxcore/util.c
index 9f1a7e28..92ad4510 100644
--- a/toxcore/util.c
+++ b/toxcore/util.c
@@ -38,7 +38,7 @@
 static uint64_t unix_time_value;
 static uint64_t unix_base_time_value;
 
-void unix_time_update()
+void unix_time_update(void)
 {
     if (unix_base_time_value == 0) {
         unix_base_time_value = ((uint64_t)time(NULL) - (current_time_monotonic() / 1000ULL));
@@ -47,7 +47,7 @@ void unix_time_update()
     unix_time_value = (current_time_monotonic() / 1000ULL) + unix_base_time_value;
 }
 
-uint64_t unix_time()
+uint64_t unix_time(void)
 {
     return unix_time_value;
 }