net: wwan: t7xx: validate port_count against message length in t7xx_port_enum_msg_handler

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

net: wwan: t7xx: validate port_count against message length in t7xx_port_enum_msg_handler

t7xx_port_enum_msg_handler() uses the modem-supplied port_count field as

a loop bound over port_msg->data[] without checking that the message buffer

contains sufficient data. A modem sending port_count=65535 in a 12-byte

buffer triggers a slab-out-of-bounds read of up to 262140 bytes.

Add a sizeof(*port_msg) check before accessing the port message header

fields to guard against undersized messages.

Add a struct_size() check after extracting port_count and before the loop.

In t7xx_parse_host_rt_data(), guard the rt_feature header read with a

remaining-buffer check before accessing data_len, validate feat_data_len

against the actual remaining buffer to prevent OOB reads and signed

integer overflow on offset.

Pass msg_len from both call sites: skb->len at the DPMAIF path after

skb_pull(), and the validated feat_data_len at the handshake path.