vswitchd: Fix unimportant memory leak.

Free dpif_names when we're done with it.

This memory leak is not a big deal since bridge_init() is only ever called
once in a given ovs-vswitchd execution.

vswitchd/bridge.c

@@ -312,6 +312,7 @@ bridge_init(void)
             dpif_close(dpif);
         }
     }
+    svec_destroy(&dpif_names);
 
     unixctl_command_register("bridge/dump-flows", bridge_unixctl_dump_flows);