fix: E1000 rx_thread scheduling — move sched_enqueue_ready outside sem lock

fix: E1000 rx_thread scheduling — move sched_enqueue_ready outside sem lock

- ksem_signal now calls sched_enqueue_ready after releasing the
  semaphore spinlock, avoiding lock-order issues when called from
  IRQ context (sched_enqueue_ready acquires sched_lock internally)
- Prevents potential deadlock: IRQ → ksem_signal → sched_lock
  while schedule() already holds sched_lock
- 35/35 smoke tests pass, cppcheck clean