Log actual address spice-server binds to

It's not always obvious what address spice-server will bind to,
in particular when the 'addr' parameter is omitted on QEMU
commandline. The decision of what address to bind to is made
in reds_init_socket with a call to getaddrinfo. Surprisingly,
that function had a call to getnameinfo() already, but it does
not seem to be using the result of that call in any way.
This commit moves this call after the socket is successfully bound
and add a log message to indicate which address it's bound to.
main_channel: fix double release of migration target data

If client_migrate_info was called once with cert-host-subject and
then again without cert-host-subject, on a third call to
client_migrate info, the cert-host-subject from the first call would
have been freed for the second time.