BUG/MINOR: check: Reinit the buffer wait list at the end of a check

BUG/MINOR: check: Reinit the buffer wait list at the end of a check

The buffer wait list is used to deal with buffer allocation failure. But at
the end of health-check, it must be reinitialized. There is no reason to
reason to get a buffer between two health-check runs. And in fact, the
associated flags, CHK_ST_IN_ALLOC and CHK_ST_OUT_ALLOC, are already cleared
at the end of a health-check.

This patch must be backported as far as 2.2. On the 2.2, MT_LIST_ADDED and
MT_LIST_DEL must be used instead of LIST_INLIST and LIST_DEL_INIT.