Fix server list announcement

Fix server list announcement

When ngircd announces the list of currently known servers
to a new (connecting) server, it sent the introducer of
the servers instead of the top server.

Assuming this network:

irc1.example.com
|--irc2.example.com
|    `--irc3.example.com
|         `--irc4.example.com
`--irc5.example.com

When irc4 connects to irc3, irc3 tells irc4 that irc5 was
connected to irc2. (irc2 had introduced irc5 to irc3; but thats
not what ngircd should have sent to the new server).

This also placed users on the wrong servers.