*: EVPN symmetric routing for IPv6 tenant routes
Implement support for EVPN symmetric routing for IPv6 routes. The next hop
for EVPN routes is the IP address of the remote VTEP which is only an IPv4
address. This means that for IPv6 symmetric routing, there will be IPv6
destinations with IPv4 next hops. To make this work, the IPv4 next hops are
converted into IPv4-mapped IPv6 addresses.
As part of support, ensure that "L3" route-targets are not announced with
IPv6 link-local addresses so that they won't be installed in the routing