upcall: Configure datapath max-revalidator through ovs-vsctl.

upcall: Configure datapath max-revalidator through ovs-vsctl.

This patch adds a new configuration option, "max-revalidator" to the
Open_vSwitch "other-config" column. This sets maximum allowed ravalidator
timeout. Actual timeout value is determined at runtime as minimum of
"max-idle" and "max-revalidator".

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>