netmem: prevent TX of unreadable skbs

In the Linux kernel, the following vulnerability has been resolved:

netmem: prevent TX of unreadable skbs

Currently on stable trees we have support for netmem/devmem RX but not

TX. It is not safe to forward/redirect an RX unreadable netmem packet

into the device's TX path, as the device may call dma-mapping APIs on

dma addrs that should not be passed to it.

Fix this by preventing the xmit of unreadable skbs.

Tested by configuring tc redirect:

sudo tc qdisc add dev eth1 ingress

sudo tc filter add dev eth1 ingress protocol ip prio 1 flower ip_proto \

tcp src_ip 192.168.1.12 action mirred egress redirect dev eth1

Before, I see unreadable skbs in the driver's TX path passed to dma

mapping APIs.

After, I don't see unreadable skbs in the driver's TX path passed to dma

mapping APIs.