ovn-northd: Fix peering of routers.

ovn-northd: Fix peering of routers.

1. Currently, the ovn-nb man page says that the 'peer'
in a logical_router_port table should point to the name
of the peer's logical router port. But the schema had declared
this column as a uuid. This looks not to be the intention as peers
for logical switches connected to routers is a name (and not a uuid).
So this patch changes the schema to be name.

2. In the southbound database, in the port_binding table, for a
logical_router_port, the peer was pointing back to itself. This
was causing ovn-controller to create patch ports where the peer
was wrongly pointing back to the source itself. This clearly looks
to be an error. So this patch fixes the peer in southbound database
to correclty point to the real peer.

3. ovn-northd.c currently skips generating logical flows to transfer
packets between two peers with comment about needing 'ARP for
neighboring routers'. It looked to me that since the router peer
is a logical object that has to be created in OVN-NB database, we
always need to statically assign the mac address. So this patch
picks the mac address from the database.

Signed-off-by: Gurucharan Shetty <guru@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>
Acked-by: Ryan Moats <rmoats@us.ibm.com>