rpc: use virNetMessageClearPayload in client

This removes the opencoded payload freeing in the client, to use
the shared virNetMessageClearPayload call. Two changes:

- ClearPayload sets nfds=0, which fixes a potential crash if
  an error path called virNetMessageFree/Clear on the message
  after fds was free'd
- We drop the inner loop VIR_FORCE_CLOSE... this may mean fds are
  kept open a little bit longer if the call is blocking but in
  practice I don't think it will have any effect

src/libvirt_remote.syms

@@ -79,6 +79,7 @@ virNetDaemonUpdateServices;
 
 # rpc/virnetmessage.h
 virNetMessageClear;
+virNetMessageClearPayload;
 virNetMessageDecodeHeader;
 virNetMessageDecodeLength;
 virNetMessageDecodeNumFDs;

src/rpc/virnetclient.c

@@ -1194,12 +1194,8 @@ virNetClientIOWriteMessage(virNetClientPtr client,
             if (rv == 0) /* Blocking */
                 return 0;
             thecall->msg->donefds++;
-            VIR_FORCE_CLOSE(thecall->msg->fds[i]);
         }
-        thecall->msg->donefds = 0;
+        virNetMessageClearPayload(thecall->msg);
-        thecall->msg->bufferOffset = thecall->msg->bufferLength = 0;
-        VIR_FREE(thecall->msg->fds);
-        VIR_FREE(thecall->msg->buffer);
         if (thecall->expectReply)
             thecall->mode = VIR_NET_CLIENT_MODE_WAIT_RX;
         else

src/rpc/virnetmessage.c

@@ -49,7 +49,7 @@ virNetMessagePtr virNetMessageNew(bool tracked)
 }
 
 
-static void
+void
 virNetMessageClearPayload(virNetMessagePtr msg)
 {
     size_t i;

src/rpc/virnetmessage.h

@@ -54,6 +54,8 @@ struct _virNetMessage {
 
 virNetMessagePtr virNetMessageNew(bool tracked);
 
+void virNetMessageClearPayload(virNetMessagePtr msg);
+
 void virNetMessageClear(virNetMessagePtr);
 
 void virNetMessageFree(virNetMessagePtr msg);