network: pf: split flush and rules commands

network: pf: split flush and rules commands

Current implementation uses a single command to flush the old rules and
create new ones. This is not optimal because if flush fails for some
non-critical reasons (e.g. because the anchor didn't previously exist),
it will block rules creation and network start.

Split this command into two: one for flush, and one for rules creation.
Also, don't fail if the flush command fails.

Signed-off-by: Roman Bogorodskiy <bogorodskiy@gmail.com>
Reviewed-by: Laine Stump <laine@redhat.com>