ovs-save: Don't always include the default flow during restore

ovs-save: Don't always include the default flow during restore

Currently the default flow (actions=NORMAL) is present in the flow table after
the flow table is restored also when the default flow is removed.

This commit changes the behaviour of the "ovs-save save-flows" command to use
"replace-flows" instead of "add-flows" to restore the flows. This is needed in
order to always have the new flow table as it was before restoring it.

Reported-by: Flavio Leitner <fbl@sysclose.org>
Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=1626096
Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>