Optimize the function of filter_send

The iov_size has been calculated in filter_send(). we can directly
return the size.In this way, this is no need to repeat calculations
in filter_redirector_receive_iov();

Signed-off-by: Lei Rao <lei.rao@intel.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Reviewed-by: Lukas Straub <lukasstraub2@web.de>
Tested-by: Lukas Straub <lukasstraub2@web.de>
Signed-off-by: Zhang Chen <chen.zhang@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/filter-mirror.c

@@ -88,7 +88,7 @@ static int filter_send(MirrorState *s,
         goto err;
     }
 
-    return 0;
+    return size;
 
 err:
     return ret < 0 ? ret : -EIO;
@@ -159,7 +159,7 @@ static ssize_t filter_mirror_receive_iov(NetFilterState *nf,
     int ret;
 
     ret = filter_send(s, iov, iovcnt);
-    if (ret) {
+    if (ret < 0) {
         error_report("filter mirror send failed(%s)", strerror(-ret));
     }
 
@@ -182,10 +182,10 @@ static ssize_t filter_redirector_receive_iov(NetFilterState *nf,
 
     if (qemu_chr_fe_backend_connected(&s->chr_out)) {
         ret = filter_send(s, iov, iovcnt);
-        if (ret) {
+        if (ret < 0) {
             error_report("filter redirector send failed(%s)", strerror(-ret));
         }
-        return iov_size(iov, iovcnt);
+        return ret;
     } else {
         return 0;
     }