The 'buf', 'sa' and 'hints' stack allocated helper variables are never
used together. Decrease the stack memory usage by scoping them off into
do-while blocks.

In this instance we do not want to use dynamic allocation as this is the
NSS module.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
---

v2: Moved two error checks containing a 'continue' out of the 'do-while'
    loop blocks

New pipeline:
https://gitlab.com/pipo.sk/libvirt/-/pipelines/986529301


 tools/nss/libvirt_nss.c | 87 ++++++++++++++++++++++++-----------------
 1 file changed, 51 insertions(+), 36 deletions(-)