libvhost-user: Fix extra vu_add/rem_mem_reg reply

Outside of postcopy mode, neither VHOST_USER_ADD_MEM_REG nor
VHOST_USER_REM_MEM_REG are supposed to send a reply unless explicitly
requested with the need_reply flag. Their current implementation always
sends a reply, even if it isn't requested. This confuses the master
because it will interpret the reply as a reply for the next message for
which it actually expects a reply.

need_reply is already handled correctly by vu_dispatch(), so just don't
send a reply in the non-postcopy part of the message handler for these
two commands.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20220407133657.155281-3-kwolf@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -800,8 +800,7 @@ vu_add_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
 
         DPRINT("Successfully added new region\n");
         dev->nregions++;
-        vmsg_set_reply_u64(vmsg, 0);
-        return true;
+        return false;
     }
 }
 
@@ -874,15 +873,13 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
         }
     }
 
-    if (found) {
-        vmsg_set_reply_u64(vmsg, 0);
-    } else {
+    if (!found) {
         vu_panic(dev, "Specified region not found\n");
     }
 
     close(vmsg->fds[0]);
 
-    return true;
+    return false;
 }
 
 static bool