code: def udp_send(udpsock, frame, address, addrlen):
          
          return lib.zsys_udp_send(udpsock, frame, address, addrlen)
docs: Send zframe to UDP socket, return -1 if sending failed due to
  interface having disappeared (happens easily with WiFi)
  *** This is for CZMQ internal use only and may change arbitrarily ***