classifier: Support table versioning

classifier: Support table versioning

This patch allows classifier rules to become visible and invisible in
specific versions.  A 'version' is defined as a positive monotonically
increasing integer, which never wraps around.

The new 'visibility' attribute replaces the prior 'to_be_removed' and
'visible' attributes.

When versioning is not used, the 'version' parameter should be passed
as 'CLS_MIN_VERSION' when creating rules, and 'CLS_MAX_VERSION' when
looking up flows.

This feature enables the support for atomic OpenFlow bundles without
significant performance penalty on 64-bit systems. There is a
performance decrease in 32-bit systems due to 64-bit atomics used.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>