bgpd: evpn path selection changes for MAC-IP SYNC route handling

bgpd: evpn path selection changes for MAC-IP SYNC route handling

When a SYNC route i.e. a route with a local ES as destination is
rxed on a switch (say L11) from an ES peer (say L12) a local
MAC/neigh entry is created on L11 with the local access port
as dest port.

Creation of the local entry triggers a local path advertisement from
L11. This could be a "locally-active" path or a "locally-inactive"
path. Inactive paths are advertised with the proxy bit.

To ensure that the local entry is not deleted by a SYNC route it is
given absolute precedence over peer-paths.

If there are two non-local paths with the same dest ES and same MM
seq number the non-proxy path is preferred. This is done to ensure
that we don't lose track of the peer-activity.

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>