set unlimited HWM for all relay devices

libzmq-3 set the default HWM for sockets to 1000 from infinite,
which can result in dropped messages on ROUTER or PUB sockets under high load.
Merge pull request #3304 from minrk/hwm

set unlimited HWM for all relay devices

libzmq-3 changed the default HWM for sockets to 1000 from infinite, which can result in dropped messages on ROUTER or PUB sockets under high load.

This PR explicitly sets these back to infinite to avoid dropped messages.

 closes #3303