Internal rename intl -> detach for LX_OPs.

"Intl" stood for "internal", which was only partially correct (eg, the
flag bit was used for lx_op_predone() requests).  With upcoming
changes, it becomes even less accurate.  "Detach" is more descriptive,
as what the bit really means is that the LX_OP is detached from its
LX_CONN's request/response stream.