qemu: Set RLIMIT_MEMLOCK when memoryBacking/locked is used

If a domain is configured to have all its memory locked, we need to set
RLIMIT_MEMLOCK so that QEMU is actually allowed to lock the memory.

src/qemu/qemu_command.c

@@ -6795,6 +6795,7 @@ qemuBuildCommandLine(virConnectPtr conn,
         virCommandAddArgFormat(cmd, "mlock=%s",
                                def->mem.locked ? "on" : "off");
     }
+    mlock = def->mem.locked;
 
     virCommandAddArg(cmd, "-smp");
     if (!(smp = qemuBuildSmpArgStr(def, qemuCaps)))