CVE-2026-31734 sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU

In the Linux kernel, the following vulnerability has been resolved: schedext: Fix isbpfmigrationdisabled false negative on non-PREEMPTRCU Since commit 8e4f0b1ebcf2 "bpf: use rcureadlockdontmigrate for trampoline.c", the BPF prolog bpfprogenter calls migratedisable only when CONFIGPREEMPTRCU is...