BUG/MINOR: proto_reverse_connect: fix preconnect with startup name resolution

BUG/MINOR: proto_reverse_connect: fix preconnect with startup name resolution

addr member of server structure is not set consistently depending on the
server address type. When using <IP:PORT> notation, its port is properly
set. However, when using <HOSTNAME:PORT>, only IP address is set after
startup name resolution but its port is left to 0.

This behavior causes preconnect to not be functional when using server
with hostname for startup name resolution. Indeed, only srv.addr is used
as connect argument through function new_reverse_conn(). To fix this,
rely on srv.svc_port : this member is always set for servers using IP or
hostname. This is similar to connect_server() on the backend side.

This does not need to be backported.