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/zio.c

@@ -2083,7 +2083,7 @@ zio_execute(zio_t *zio)
  * enough to allow zio_execute() to be called recursively.  A minimum
  * stack size of 16K is required to avoid needing to re-dispatch the zio.
  */
-boolean_t
+static boolean_t
 zio_execute_stack_check(zio_t *zio)
 {
 #if !defined(HAVE_LARGE_STACKS)