IB/core: Temporarily disable create_flow/destroy_flow uverbs

IB/core: Temporarily disable create_flow/destroy_flow uverbs

The create_flow/destroy_flow uverbs and the associated extensions to
the user-kernel verbs ABI are under review and are too experimental to
freeze at this point.

So userspace is not exposed to experimental features and an uinstable
ABI, temporarily disable this for v3.12 (with a Kconfig option behind
staging to reenable it if desired).

The feature will be enabled after proper cleanup for v3.13.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Link: http://marc.info/?i=cover.1381351016.git.ydroneaud@opteya.com
Link: http://marc.info/?i=cover.1381177342.git.ydroneaud@opteya.com
[ Add a Kconfig option to reenable these verbs.  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>