agent: add nice_agent_get_sockets API
This API makes it possible to get an array of all of the sockets used by a specific component, this is useful to set options on the socket.
Also bump GLib requirement to 2.54, which is the version in RHEL 7
This API makes it possible to get an array of all of the sockets used by a specific component, this is useful to set options on the socket.
Also bump GLib requirement to 2.54, which is the version in RHEL 7