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.