context: only apply lock-quantum for unsuspended nodes

When the node is suspended, don't take into account the lock-quantum
settings or else the graph would not want to change to the requested
quantum of the node.

Say we have a jack node with node.lock-quantum = true and
node.latency=256/48000. When it joins the graph and is suspended, the
lock-quantum is ignored and the node.latency is set on the graph.
After that, the lock-quantum ensures the graph quantum doesn't change
anymore until the node is suspended.