dpif-netdev: Take non_pmd_mutex to access tx cached ports.

As documented in dp_netdev_pmd_thread, we must take non_pmd_mutex to
access the tx port caches for the non pmd thread.

Found by inspection.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>

Author: ddiproietto

lib/dpif-netdev.c

@@ -3369,8 +3369,10 @@ dp_netdev_del_pmd(struct dp_netdev *dp, struct dp_netdev_pmd_thread *pmd)
     /* NON_PMD_CORE_ID doesn't have a thread, so we don't have to synchronize,
      * but extra cleanup is necessary */
     if (pmd->core_id == NON_PMD_CORE_ID) {
+        ovs_mutex_lock(&dp->non_pmd_mutex);
         emc_cache_uninit(&pmd->flow_cache);
         pmd_free_cached_ports(pmd);
+        ovs_mutex_unlock(&dp->non_pmd_mutex);
     } else {
         latch_set(&pmd->exit_latch);
         dp_netdev_reload_pmd__(pmd);