idpf: fix null-ptr-deref in idpf_features_check

In the Linux kernel, the following vulnerability has been resolved: idpf: fix null-ptr-deref in idpf_features_check idpf_features_check is used to validate the TX packet. skb header length is compared with the hardware supported value received from the device control plane. The value is stored in the adapter structure and to access it, vport pointer is used. During reset all the vports are released and the vport pointer that the netdev private structure points to is NULL. To avoid null-ptr-deref, store the max header length value in netdev private structure. This also helps to cache the value and avoid accessing adapter pointer in hot path. BUG: kernel NULL pointer dereference, address: 0000000000000068 ... RIP: 0010:idpf_features_check+0x6d/0xe0 [idpf] Call Trace: <TASK> ? __die+0x23/0x70 ? page_fault_oops+0x154/0x520 ? exc_page_fault+0x76/0x190 ? asm_exc_page_fault+0x26/0x30 ? idpf_features_check+0x6d/0xe0 [idpf] netif_skb_features+0x88/0x310 validate_xmit_skb+0x2a/0x2b0 validate_xmit_skb_list+0x4c/0x70 sch_direct_xmit+0x19d/0x3a0 __dev_queue_xmit+0xb74/0xe70 ...