[BUG] fix missing parenthesis in check_response_for_cacheability

Parenthesis were missed when code was moved to this function.
This results in non-cacheable transactions not being ignored.
diff --git a/src/proto_http.c b/src/proto_http.c
index 99bef1b..feed6cc 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -4475,7 +4475,7 @@
 	char *cur_ptr, *cur_end, *cur_next;
 	int cur_idx;
 
-	if (!txn->flags & TX_CACHEABLE)
+	if (!(txn->flags & TX_CACHEABLE))
 		return;
 
 	/* Iterate through the headers.