* add receive hook - if set, this function is called when request is finished
* unstatic smb_rq_enqueue(), smb_rq_reply() so that code can use that
independant of smb_rq_simple() et al
this is needed for NT DIRECTORY CHANGE NOTIFY SMB, since they typically
take very long to complete and we want to be able to use single kernel thread
to handle them all
add support for 'nowait' requests (flag SMBR_NOWAIT), which don't expect
and answer from server and are marked as 'processed' immediatelly
after they are sent to server - needed for NT CANCEL SMB