Etiquette when a student attends a conference with his/her supervisor

There's no ethical dilemma here. You might tag along with him at first to let him introduce you to some people in the field he knows, but after awhile of that, you should feel free to introduce yourself to people who look to be more your age or status (younger looking people are more likely to be students like yourself). Also, at the dinner, you should feel free to introduce yourself to people whose talks you attended and the people at your table.

The above assumes you are comfortable in such social situations. Not everything at a conference is business. Network and enjoy the social aspects of the events if you can.

Let your advisor advise you, i.e. ask.

At which occasions does he/she expect you close by? It is far better to discuss this once before the conference than you having to bother him/her five times a day.

you are both there to network -- that means he want to talk people other than you, and he expects you to talk to people other than him.