CVE-2026-64034: net: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer

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

net: mana: Fix TOCTOU double-fetch of hwcmsgid from DMA buffer

In manahwcrxeventhandler(), resp->response.hwcmsgid is read from DMA-coherent memory and bounds-checked, then manahwchandleresp() re-reads the same field from the same DMA buffer for testbit() and pointer arithmetic.

DMA-coherent memory is mapped uncacheable on x86 and is shared, unencrypted, in Confidential VMs (SEV-SNP/TDX), so each load goes directly to host-visible memory. A H/W can modify the value between the check and the use, bypassing the bounds validation.

Fix this by reading hwcmsgid exactly once using READONCE() into a stack-local variable in manahwcrxeventhandler(), and passing the validated value as a parameter to manahwchandleresp().