Support local preference and sequence for EVPN routes

These attributes are required to support live migration.
They are already supported for IPv4 and IPv6 routes, so
EVPN can just reuse the existing infrastructure.

Change-Id: I6c0623d61f936d29578ec4006440a1ac2b2d5b99
Partial-Bug: 1403602
Merge "Support local preference and sequence for EVPN routes"