ofproto: Allow bundle idle timeout to be configured.

ofproto: Allow bundle idle timeout to be configured.

In some cases 10 seconds might be too much time and in
other cases it might be too little.

The OpenFlow spec mandates that it should wait at least one
second, so enforce that as the minimum acceptable value.

Signed-off-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>