/*
* rt_msg2
*
* fills 'cp' or 'w'.w_tmem with the routing socket message and
* returns the length of the message in 'lenp'.
*
* if walkarg is 0, cp is expected to be 0 or a buffer large enough to hold
* the message
* otherwise walkarg's w_needed is updated and if the user buffer is
* specified and w_needed indicates space exists the information is copied
* into the temp space (w_tmem). w_tmem is [re]allocated if necessary,
* if the allocation fails ENOBUFS is returned.
*/