Give the fellow open worker thread some state

To address some Coverity pedentry with minor impact (at most)

CID#469230

src/fellow_storage.c

@@ -2211,9 +2211,18 @@ dummy_ban(void)
 	return (ban);
 }
 
+enum sfe_open_worker_state {
+	SOW_INIT = 0,
+	SOW_STARTING,
+	SOW_RUNNING,
+	SOW_STOPPING,
+	SOW_DONE
+};
+
 struct sfe_open_worker_priv {
 	unsigned			magic;
 #define SFE_OPEN_WORKER_PRIV		0xe4711115
+	enum sfe_open_worker_state	state;
 
 	pthread_mutex_t			mtx;
 	pthread_cond_t			cond;
@@ -2231,9 +2240,13 @@ sfe_open_worker_thread(struct worker *wrk, void *priv)
 	AZ(pthread_mutex_lock(&sow->mtx));
 	AZ(sow->wrk);
 	sow->wrk = wrk;
+	assert(sow->state == SOW_STARTING);
+	sow->state = SOW_RUNNING;
 	AZ(pthread_cond_signal(&sow->cond));
-	AZ(pthread_cond_wait(&sow->cond, &sow->mtx));
+	while (sow->state < SOW_STOPPING)
+		AZ(pthread_cond_wait(&sow->cond, &sow->mtx));
 	AZ(sow->wrk);
+	sow->state = SOW_DONE;
 	AZ(pthread_mutex_unlock(&sow->mtx));
 	return (NULL);
 }
@@ -2247,9 +2260,12 @@ sfe_open_worker_init(struct sfe_open_worker_priv *sow)
 	AZ(pthread_cond_init(&sow->cond, NULL));
 
 	AZ(pthread_mutex_lock(&sow->mtx));
+	assert(sow->state == SOW_INIT);
+	sow->state = SOW_STARTING;
 	WRK_BgThread(&sow->thr, "sfe-open-worker",
 	    sfe_open_worker_thread, sow);
-	AZ(pthread_cond_wait(&sow->cond, &sow->mtx));
+	while (sow->state < SOW_RUNNING)
+		AZ(pthread_cond_wait(&sow->cond, &sow->mtx));
 	AN(sow->wrk);
 	//lint -e{454} mutex
 	return (sow->wrk);
@@ -2271,6 +2287,10 @@ sfe_open_worker_fini(struct sfe_open_worker_priv *sow)
 	Pool_Sumstat(sow->wrk);
 
 	sow->wrk = NULL;
+
+	assert(sow->state == SOW_RUNNING);
+	sow->state = SOW_STOPPING;
+
 	AZ(pthread_cond_signal(&sow->cond));
 	//lint -e{455} mutex
 	AZ(pthread_mutex_unlock(&sow->mtx));