res_crypto: Perform cleanup at shutdown.

This change causes res_crypto to unregister CLI at shutdown while still
preventing the module from being unloaded.

ASTERISK-25673 #close

Change-Id: Ie5d57338dc2752abfc0dd05d0eec86413f2304fc

res/res_crypto.c

@@ -652,13 +652,17 @@ static int load_module(void)
 	} else {
 		crypto_load(-1, -1);
 	}
+
+	/* This prevents dlclose from ever running, but allows CLI cleanup at shutdown. */
+	ast_module_shutdown_ref(ast_module_info->self);
 	return AST_MODULE_LOAD_SUCCESS;
 }
 
 static int unload_module(void)
 {
-	/* Can't unload this once we're loaded */
-	return -1;
+	ast_cli_unregister_multiple(cli_crypto, ARRAY_LEN(cli_crypto));
+
+	return 0;
 }
 
 /* needs usecount semantics defined */