fix the namespace error in net.cpp to make mpi-related code compile ok
fix the namespace error in net.cpp to make mpi-related code compile ok

zhengsx/multiverso,liming-vie/multiverso,Microsoft/multiverso,you-n-g/multiverso,liming-vie/multiverso,zhengsx/multiverso,Microsoft/multiverso,liming-vie/multiverso,liming-vie/multiverso,Microsoft/multiverso,you-n-g/multiverso,zhengsx/multiverso,you-n-g/multiverso,Microsoft/multiverso,zhengsx/multiverso,you-n-g/multiverso