Add a call to posix_fadvise() to indicate to the kernel, that `named`
won't be needing the dumped zone files any time soon with:
* POSIX_FADV_DONTNEED - The specified data will not be accessed in the
near future.
Notes:
POSIX_FADV_DONTNEED attempts to free cached pages associated with the
specified region. This is useful, for example, while streaming large
files. A program may periodically request the kernel to free cached
data that has already been used, so that more useful cached pages are
not discarded instead.
e83b6569da