poll-loop: Set poll loop initial deadline to LLONG_MAX.

This is consistent with the re-initialization value that poll_block() uses.
It is better than 0 because the monotonic clock can have a negative value,
even though that is rare and pathological.

Found by inspection.

Acked-by: Justin Pettit <jpettit@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/poll-loop.c

@@ -415,6 +415,7 @@ poll_loop(void)
     loop = pthread_getspecific(key);
     if (!loop) {
         loop = xzalloc(sizeof *loop);
+        loop->timeout_when = LLONG_MAX;
         hmap_init(&loop->poll_nodes);
         xpthread_setspecific(key, loop);
     }