ofproto: Add a fixed bundle idle timeout of 10 seconds.

ofproto: Add a fixed bundle idle timeout of 10 seconds.

Timing out idle bundles frees memory that would effectively be leaked
if a long standing OpenFlow connection would fail to commit or discard
a bundle.

OpenFlow specification mandates the timeout to be at least one second,
if the switch implements such a timeout.  This patch makes the bundle
idle timeout to be 10 seconds.

We do not limit the number of messages in a bundle, so it does not
make sense to limit the number of bundles either, especially now that
idle bundles are timed out.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>