kernel: net: avoid potential underflow in qdisc_pkt_len_init() with UFO

In the Linux kernel, the following vulnerability has been resolved: net: avoid potential underflow in qdiscpktleninit with UFO After commit 7c6d2ecbda83 "net: be more gentle about silly gso requests coming from user" virtionethdrtoskb had sanity check to detect malicious attempts from user space ...