main/zeromq: build with CURVE security support again

Support for CURVE security was silently dropped with the upgrade to version 4.3.5 as upstream changed the default of ENABLE_CURVE as part of this release [1]. Since the 4.3.5 release, zeromq is therefore also not linked against libsodium anymore but as libsodium is still in $makedepends I believe this to be unintentional.

Also: py3-pyzmq fails check() without this which is how this was discovered. Alternatively, we could also patch py3-pyzmq to not assume that libzmq provides CURVE security support.