CVE-2026-98059 bpf: Mark sched_process_wait argument as nullable

In the Linux kernel, the following vulnerability has been resolved: bpf: Mark schedprocesswait argument as nullable dowait passes wo-wopid to the schedprocesswait tracepoint. kernelwait4 leaves wopid NULL for wait4-1, and kernelwaitidprepare does likewise for waitidPALL. btfctxaccess currently...