Bluetooth: btnxpuart: Validate the FW dump header length

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

Bluetooth: btnxpuart: Validate the FW dump header length

nxp_process_fw_dump() pulls the ACL header off the frame and then reads
seq_num and buf_len from a struct nxp_fw_dump_hdr placed at skb->data,
without checking that the ACL payload is long enough to contain it.

h4_recv_buf() collects HCI_ACL_HDR_SIZE bytes of header followed by the
number of payload bytes named in that header, so skb->len is 4 + dlen
with dlen supplied by the controller and possibly smaller than the 8
byte dump header, or zero. A short frame with connection handle 0xfff
therefore reads both fields from beyond the received data.

Beyond the read itself, buf_len is what terminates a dump: a value of
zero makes the driver call hci_devcd_complete() and reset the
controller, so a truncated frame can end a dump early.

Use skb_pull_data() to validate and pull the FW dump header before
accessing its fields. Warn and reject the chunk if the header is
truncated.