wifi: libipw: reject too-short beacon and probe responses

In the Linux kernel, the following vulnerability has been resolved: wifi: libipw: reject too-short beacon and probe responses libipw_process_probe_response() and the libipw_network_init() call it makes assume the frame contains the full 36-byte beacon and probe response prefix, but the ipw2100 and ipw2200 receive paths only establish that a management frame carries the generic 24-byte three-address header. libipw_network_init() then computes the information element length as stats->len - sizeof(*beacon) stats->len is a u16 and sizeof() has type size_t, so the subtraction is evaluated as size_t and wraps instead of going negative. Truncating that to the u16 length parameter of libipw_parse_info_param() yields 65524 for a 24-byte beacon, and the parser then walks the receive buffer as if it held almost 64 KiB of information elements, reading past the allocation. Reject the frame before any fixed field is touched. Found by an AI-assisted review of length arithmetic in management frame parsers. Verified with a KUnit case under Generic KASAN on arm64 under QEMU; I do not have the hardware, so it is not tested on a real device.