Mark functions as static

Mark functions used only in the same translation unit as static. This
only includes functions that do not have a prototype in a header file
either.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

module/zfs/dbuf.c

@@ -588,7 +588,7 @@ dbuf_is_metadata(dmu_buf_impl_t *db)
  * distributed between all sublists and uses this assumption when
  * deciding which sublist to evict from and how much to evict from it.
  */
-unsigned int
+static unsigned int
 dbuf_cache_multilist_index_func(multilist_t *ml, void *obj)
 {
 	dmu_buf_impl_t *db = obj;