ZMQ_FILTER option removed

The filtering is now done depending on the socket type. SUB socket
filters the messages (end-to-end filtering) while XSUB relies
on upstream nodes to do (imprefect) filtering.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/sub.cpp

@@ -25,6 +25,10 @@ zmq::sub_t::sub_t (class ctx_t *parent_, uint32_t tid_) :
     xsub_t (parent_, tid_)
 {
     options.type = ZMQ_SUB;
+
+    //  Switch filtering messages on (as opposed to XSUB which where the
+    //  filtering is off).
+    options.filter = true;
 }
 
 zmq::sub_t::~sub_t ()