ofproto: Handle (draft) OpenFlow 1.5 insert and remove group commands.

Handle (draft) OpenFlow 1.5 insert and remove group commands
of group mod messages.

ONF-JIRA: EXT-350
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
ovs-ofctl: Support bucket commands

(Draft) OpenFlow 1.5 flow mod commands include commands to manipulate the
buckets of existing groups. This patch add support to ovs-ofctl for these
commands. It also adds documentation and tests for them.

ONF-JIRA: EXT-350
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>