ofproto: Use OFPRR_GROUP_DELETE

Use OFPRR_GROUP_DELETE as the reason for deleting flows due
to the removal of a group that they use.

This implementation adds an delete_reason member to struct ofputil_flow_mod
as a convenient way to set the reason used by delete_flows__() when it is
called indirectly from delete_group__().

Signed-off-by: Simon Horman <horms@verge.net.au>
[blp@nicira.com initialized the new member in a few more places]
Signed-off-by: Ben Pfaff <blp@nicira.com>

lib/ofp-util.h

@@ -307,6 +307,9 @@ struct ofputil_flow_mod {
     enum ofputil_flow_mod_flags flags;
     struct ofpact *ofpacts;  /* Series of "struct ofpact"s. */
     size_t ofpacts_len;      /* Length of ofpacts, in bytes. */
+
+    /* Reason for delete; ignored for non-delete commands */
+    enum ofp_flow_removed_reason delete_reason;
 };
 
 enum ofperr ofputil_decode_flow_mod(struct ofputil_flow_mod *,