migration/multifd: Fix leaking of Error in TLS error flow

migration/multifd: Fix leaking of Error in TLS error flow

If there is an error in multifd TLS handshake task,
multifd_tls_outgoing_handshake() retrieves the error with
qio_task_propagate_error() but never frees it.

Fix it by freeing the obtained Error.

In addition, the error is not reported at all, so report it with
migrate_set_error().

Fixes: 29647140157a ("migration/tls: add support for multifd tls-handshake")
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20231231093016.14204-8-avihaih@nvidia.com
Signed-off-by: Peter Xu <peterx@redhat.com>