include/types: move operator<< into the proper namespace

include/types: move operator<< into the proper namespace

we should define the operator<< in the namespace of its 2nd parameter.

normally, the operator<< defined in the global namespace works. but
there is a subtle difference between the operator<< defined in std
namespace and the global one because of Koenig lookup.

Signed-off-by: Kefu Chai <kchai@redhat.com>