Memory disclosure via unvalidated net pkt pointer

Improper input validation in Zephyr RTOS before 3.3 allows local users with shell access to read firmware memory or crash the device. The net pkt command's cmd_net_pkt handler converts a hexadecimal string to a pointer and passes it to net_pkt_buffer_info and net_pkt_buffer_hexdump without verifying that it identifies a valid net_pkt object. Successful disclosure requires knowledge of the memory layout and attacker-controlled data at a known address; an arbitrary invalid address can instead fault and crash the device.