pbrd: properly handle duplicate set vrf XX configs

pbrd: properly handle duplicate set vrf XX configs

Properly handle the case where we are sent the same `set vrf`
configs for a pbr map repeatedly. If we are sent the same
config, we return successfully without doing anyting.

If the config is different and its not a [no], then return failure
as we did before since we don't support atomic replace yet.

Before, we would fail anytime even if the config sent was the same
as is already there. This would cause frr-reload to mark as a
failure when it tried to re-apply the same config.

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>