net: macb: drop in-flight Tx SKBs on close

In the Linux kernel, the following vulnerability has been resolved: net: macb: drop in-flight Tx SKBs on close The MACB driver has since forever leaked the outgoing SKBs that have not yet been marked as completed. They live in queue->tx_skb which gets freed without remorse nor checking. macb_free_consistent() gets called in a few codepaths, but only close will trigger the added expressions. In macb_open() and macb_alloc_consistent() failure cases, queues' tx_skb just got allocated and are empty.