NetworkPkg/Ip4Dxe: fix NetLibDestroyServiceChild() call
    
    Both NetLibDestroyServiceChild() and EFI_SERVICE_BINDING_DESTROY_CHILD
    take an EFI_HANDLE for the "ChildHandle" parameter, not an (EFI_HANDLE*).
    
    This patch fixes a real bug.
    
    Cc: Jiaxin Wu <jiaxin.wu@intel.com>
    Cc: Siyuan Fu <siyuan.fu@intel.com>
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>