CVE-2026-64125: net: bcmgenet: keep RBUF EEE/PM disabled

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

net: bcmgenet: keep RBUF EEE/PM disabled

Setting RBUFEEEEN | RBUFPMEN in RBUFENERGYCTRL breaks the RX path on GENET hardware once MAC EEE becomes active. RX traffic stops flowing while the link stays up and the usual descriptor/RX error counters remain quiet. In that state the MAC still accepts frames (rbufovflowcnt keeps climbing) but RBUF no longer forwards them to DMA, so rxpackets is no longer incremented at the netdev level. On some boards the corruption ends up as a paging fault in skbreleasedata via bcmgenetrxpoll on an LPI exit.

Reproduced on Pi 4B (BCM2711 + BCM54213PE) and confirmed by Florian Fainelli on an internal Broadcom 4908-family board with the same crash signature. RBUFPMEN is not publicly documented.

This shows up more often now that physupporteee() enables EEE by default, but it also affects older kernels as soon as TX LPI is turned on via ethtool, so it is not specific to recent changes.

Always clear RBUFEEEEN | RBUFPMEN in bcmgeneteeeenableset so the bits stay off across resets. UMAC and TBUF setup is left alone so TX-side EEE keeps working.