Legacy code in 'ssh_set_callbacks' will fallback to
'ssh_legacy_log_callback' (if the current log cb is
NULL) setting the user data to the current session.
However, if any other session is created afterwards,
it won't update the user data with the new session,
potentially leading to a use-after-free.
Fixes#238.
Signed-off-by: Diego Roux <diegoroux04@protonmail.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
46a28cfc49