CVE-2026-74286: net: pfcp: allocate per-cpu tstats for PFCP netdevs

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

net: pfcp: allocate per-cpu tstats for PFCP netdevs

PFCP uses devgettstats64() as its ndogetstats64 callback, but pfcplinksetup() does not request NETDEVPCPUSTATTSTATS. The net core therefore leaves dev->tstats NULL for PFCP devices.

Creating a PFCP rtnetlink device can immediately ask the new netdev for stats while building the RTMNEWLINK notification. That reaches devgettstats64() and dereferences the NULL dev->tstats pointer.

Set pcpustattype to NETDEVPCPUSTATTSTATS during PFCP link setup so the net core allocates the storage expected by devgettstats64().