Bring EVPN NLRI support up to the latest draft.

Add support for EthernetSegmentId.
Implement parse and build for all 4 route types.
Implement sanity checks for EVPN NLRI.
Implement PMSI Tunnel attribute.
EVPN interoperability with JUNOS.

Add EvpnManager class to handle translation of a broadcast MAC route
from an agent into a Inclusive Multicast route.  This class also has
glue logic to build an ingress replication OList for each agent.

Use evpn tables instead of enet tables for VRFs.
Implement OriginatorId attribute and set it the same value as nexthop
to work around a JUNOS bug.
Implement Params attribute to store arbitrary parameter flags.
Implement test infrastructure to simulate EVPN PEs that don't support
edge replication.
Tweak XMPP messages to carry a couple of extra fields.

Add unit tests for EvpnManager.
Add new integration tests to bgp_xmpp_evpn_test.cc.
Add new tests to evpn_tables_test.cc.
Add new tests to bgp_attr_test.cc.

Change-Id: I408339cb06627ef1164c37b3e67a9e35e7a5b178