qemu-sockets: use qapi_free_SocketAddress in cleanup

Commit 74b6ce43e3 uses the wrong free API for a SocketAddress, that
may leak some linked data.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20160706164246.22116-1-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
