ign-transport9 debbuilds failing on debian buster

[scpeters]

Environment

• OS Version: debian Buster
• debbuild for 9.1.0

Description

• Expected behavior: expect debbuild to succeed
• Actual behavior: it fails

Steps to reproduce

1. rebuild the following job: https://build.osrfoundation.org/job/ign-transport9-debbuilder/175/

Output

/var/lib/jenkins/workspace/ign-transport9-debbuilder/build/ignition-transport-9.1.0/src/NodeShared.cc:98:16: error: ‘send_flags’ in namespace ‘zmq’ does not name a type
     const zmq::send_flags &_type)
                ^~~~~~~~~~

Per gazebo-tooling/release-tools#297, this may require a port of #159

[chapulina]

I believe #159 is already in ign-transport9, I see lots of IGN_CPPZMQ_POST_4_7_0s in that branch.

[scpeters]

I believe #159 is already in ign-transport9, I see lots of IGN_CPPZMQ_POST_4_7_0s in that branch.

you're right; I see them too. I don't know what else is needed then