kernel: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu()

A flaw was found in the Linux kernel's Virtual Extensible LAN VXLAN module. This vulnerability occurs because a cached IP header pointer is improperly reused after a Path Maximum Transmission Unit PMTU check. When the packet's head is modified during the PMTU check, the old cached IP header point...