The _aaaa_iiii_oooo______hhhh_oooo_llll_dddd_((((_)))) function allows the calling process to defer or resume the
reception of callback notification invocations. If the should_hold
parameter is _AAAA_IIII_OOOO______HHHH_OOOO_LLLL_DDDD______CCCC_AAAA_LLLL_LLLL_BBBB_AAAA_CCCC_KKKK, callbacks will be deferred. If the
should_hold parameter is _AAAA_IIII_OOOO______RRRR_EEEE_LLLL_EEEE_AAAA_SSSS_EEEE______CCCC_AAAA_LLLL_LLLL_BBBB_AAAA_CCCC_KKKK_SSSS then callbacks will be
released. If the value is _AAAA_IIII_OOOO______IIII_SSSS_HHHH_EEEE_LLLL_DDDD______CCCC_AAAA_LLLL_LLLL_BBBB_AAAA_CCCC_KKKK_SSSS then nothing is done and
the current state is returned. Callbacks are the MIPS ABI preferred
method for notifications for completions of asynchronous I/O operations.