Update zmq/core/socket.pyx
Update zmq/core/socket.pyx

IPC_PATH_MAX_LEN is not always defined.
swn1/pyzmq,ArvinPan/pyzmq,Mustard-Systems-Ltd/pyzmq,ArvinPan/pyzmq,dash-dash/pyzmq,ArvinPan/pyzmq,caidongyun/pyzmq,Mustard-Systems-Ltd/pyzmq,dash-dash/pyzmq,Mustard-Systems-Ltd/pyzmq,caidongyun/pyzmq,swn1/pyzmq,dash-dash/pyzmq,swn1/pyzmq,caidongyun/pyzmq,yyt030/pyzmq,yyt030/pyzmq,yyt030/pyzmq