OFStateManager: gentable register/unregister
OFStateManager: gentable entry add
OFStateManager: refactor gentable testcase
OFStateManager: clear gentable on unregister
OFStateManager: gentable entry deletion
OFStateManager: gentable modify
OFStateManager: parse value in gentable utest
OFStateManager: gentable clear
OFStateManager: gentable entry stats
OFStateManager utest: test a single gentable
OFStateManager: implement test gentable

This is provided to ease writing OFTests for the gentable infrastructure.
OFStateManager: gentable desc stats request
OFStateManager: gentable table desc stats / stats handlers
OFStateManager: keep track of gentable num_entries
OFStateManager: add gentable bucket stats handler
OFStateManager: implement gentable set buckets size handler
OFStateManager: use append_bind for gentable stats when possible
OFStateManager: add ind_core_gentable_spawn_iter_task

Also use it from the clear request handler.

The interface is similar to the flowtable iter task.
OFStateManager: convert gentable entry stats to a long running task
OFStateManager: convert gentable entry desc stats to a long running task