Use wake_with scheme in order not to wake w/ the lock held

This way it's possible to wake a thread while holding the lock
that protects the thread pointer of going away. The lock itself
won't be held by the waker and thus the wakee will be able to
use it immedietly w/o ctx. Suggested by Nadav.

drivers/virtio-blk.cc

@@ -175,9 +175,10 @@ void virtio_blk::response_worker() {
         // wake up the requesting thread in case the ring was full before
         _request_thread_lock.lock();
         if (_waiting_request_thread) {
-            _waiting_request_thread->wake();
+           _waiting_request_thread->wake_with([&] { _request_thread_lock.unlock(); });
+        } else {
+            _request_thread_lock.unlock();
         }
-        _request_thread_lock.unlock();
     }
 }