unbound: redirect after save

PR: https://forum.opnsense.org/index.php?topic=1490.0
(cherry picked from commit 811a3287)

src/www/services_unbound.php

@@ -136,6 +136,8 @@ if ($_POST) {
 		if (!$input_errors) {
 			write_config("DNS Resolver configured.");
 			mark_subsystem_dirty('unbound');
+			header("Location: services_unbound.php");
+			exit;
 		}
 	}
 }