omzmq: make BIND mode work

For this, I added an addtl zocket parameter to pData, which is used
in BIND mode (as it is the sole one!). I don't have a test env, so
there may even be some compile time errors. Also, I may have overlooked
a zocket instance. That means someone else must verify my changes. They
should be good enough though, to get you guys going ;)