raidz_test: Restore rand_data protection

It feels dirty to modify protection of a memory allocated via libc,
but at least we should try to restore it before freeing.

Signed-off-by: Alexander Motin <[email protected]>

Author: amotin

cmd/raidz_test/raidz_test.c

@@ -848,6 +848,8 @@ main(int argc, char **argv)
 		err = run_test(NULL);
 	}
 
+	mprotect(rand_data, SPA_MAXBLOCKSIZE, PROT_READ | PROT_WRITE);
+
 	umem_free(rand_data, SPA_MAXBLOCKSIZE);
 	kernel_fini();