Change the flags that are set for a callback on a buffer by adding more.
@param buffer the evbuffer that the callback is watching.
@param cb the callback whose status we want to change.
@param flags EVBUFFER_CB_ENABLED to re-enable the callback.
@return 0 on success, -1 on failure.
Change the flags that are set for a callback on a buffer by adding more.
@param buffer the evbuffer that the callback is watching. @param cb the callback whose status we want to change. @param flags EVBUFFER_CB_ENABLED to re-enable the callback. @return 0 on success, -1 on failure.