Add 'bev' to the list of bufferevents whose aggregate reading and writing
is restricted by 'g'. If 'g' is NULL, remove 'bev' from its current group.
A bufferevent may belong to no more than one rate-limit group at a time.
If 'bev' is already a member of a group, it will be removed from its old
group before being added to 'g'.
Add 'bev' to the list of bufferevents whose aggregate reading and writing is restricted by 'g'. If 'g' is NULL, remove 'bev' from its current group.
A bufferevent may belong to no more than one rate-limit group at a time. If 'bev' is already a member of a group, it will be removed from its old group before being added to 'g'.
Return 0 on success and -1 on failure.