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

cmd/zpool/zpool_vdev.c

@@ -1173,7 +1173,7 @@ is_grouping(const char *type, int *mindev, int *maxdev)
  * Note: we don't bother freeing anything in the error paths
  * because the program is just going to exit anyway.
  */
-nvlist_t *
+static nvlist_t *
 construct_spec(nvlist_t *props, int argc, char **argv)
 {
 	nvlist_t *nvroot, *nv, **top, **spares, **l2cache;