ovs-vsctl: Speed up port management operations with many ports.
This makes a sequence of 10,000 "add-port" operations on a single ovs-vsctl
command line about 4X faster. It makes a sequence of 10,000 "del-port"
operations on a single command line over 2X faster.
It works by not repopulating the cache of relationships between bridges,
ports, and interfaces after most operations, instead updating them
incrementally in-place.