CLEANUP: ssl: use pool_zalloc() in ssl_init_keylog()

This one used to alloc then zero the area, let's have the allocator do it.
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 83b9d11..527ec80 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -1788,12 +1788,10 @@
 	if (SSL_get_ex_data(ssl, ssl_keylog_index))
 		return;
 
-	keylog = pool_alloc(pool_head_ssl_keylog);
+	keylog = pool_zalloc(pool_head_ssl_keylog);
 	if (!keylog)
 		return;
 
-	memset(keylog, 0, sizeof(*keylog));
-
 	if (!SSL_set_ex_data(ssl, ssl_keylog_index, keylog)) {
 		pool_free(pool_head_ssl_keylog, keylog);
 		return;