do not inline smb_iod_rqprocessed()
make smb_iod_sendall(), smb_iod_recvall() 'return' void - the return value
was always ignored
smb_iod_recvall(): turn an programming error condition check to KASSERT()
smb_iod_main(): g/c unused 'error' local
smb_iod_thread(): iod_p is assigned in smb_iod_create(), so just KASSERT()
it's correct here