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_stats.c

@@ -61,7 +61,7 @@ dbuf_stats_hash_table_headers(char *buf, size_t size)
 	return (0);
 }
 
-int
+static int
 __dbuf_stats_hash_table_data(char *buf, size_t size, dmu_buf_impl_t *db)
 {
 	arc_buf_info_t abi = { 0 };