max_sockets references incorrect ZMQ_MAXMSGSIZE

[James Vanns]

This line;
using max_sockets = opt::integer<ZMQ_MAXMSGSIZE>;
Should probably be;
using max_sockets = opt::integer<ZMQ_MAX_SOCKETS>;
See here;
https://github.com/zeromq/azmq/blob/master/azmq/detail/context_ops.hpp#L31

I needed to increase this for subscribing to >1000 channels/topics and found that it didn't work - because of this bug. Changing it locally and recompiling had the desired effect. Incidentally, I think the project (which is great BTW) would benefit from a few examples on how to properly set context options ;)

[James Vanns]

Here, I created a pull request; #191

[Adam Boseley]

change merged