tools: Fix unnecessary routing perturbations due to old style config

tools: Fix unnecessary routing perturbations due to old style config

Ticket: CM-14060
Reviewed By:
Testing Done:

There are two harmful problems (cause routing changes in the network) with the
2.5.x style config:
    one with the old style specification of "multipath as-relax", and
    the other with ip import-table, used by redistribute neighbor

In 2.5, we had the user specify 'no-as-set' as the suffix to
'bgp bestpath as-path multipath relax' to avoid quagga's default behavior
which'd cause weird routing problems. However, in 3.x, we made 'no-as-set' as
the default, and so its neither required to specify it nor is it shown in the
running config. This means when we do quagga reload, we remove the multipath
as-relax line and add it back with the no-as-set line. This causes all BGP
sessions to be reset.

The problem with the "ip import-table" is that it causes us to unimport the
routes and then add it back again, causing routing prefix changes throughout
the network, potentially causing blackholing of traffic.

This fix addresses both these issues and avoids the unnecessary routing blips.

Signed-off-by: Dinesh Dutt <ddutt@cumulusnetworks.com>