core: increase file-caching

Same value than the network one. In order to fix low-fps video with high cpu
count, as decided during the last technical meeting.

cf. background here:
https://mailman.videolan.org/pipermail/vlc-devel/2019-September/127432.html

Author: tguillem

src/libvlc-module.c

@@ -1861,7 +1861,7 @@ vlc_module_begin ()
 
     set_section( N_( "Advanced" ), NULL )
 
-    add_integer( "file-caching", DEFAULT_PTS_DELAY / 1000,
+    add_integer( "file-caching", CLOCK_FREQ / 1000,
                  CACHING_TEXT, CACHING_LONGTEXT, true )
         change_integer_range( 0, 60000 )
         change_safe()