lib: fix prefix-list entry update

lib: fix prefix-list entry update

When a prefix-list entry is updated, current NB code calls the
replacement code multiple times, once per each updated field. It means
that when multiple fields of an entry are changed in a single commit,
the replacement is done with an interim state of a prefix-list instead
of a final one. To fix the issue, we should call the replacement code
once, after all fields of an entry are updated.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>
(cherry picked from commit 0bc2ab8598fa1418d3a45499e4f047622d21d6b4)