io: Add a read flag for relaxed EOF

io: Add a read flag for relaxed EOF

Add a read flag that can inform a channel that it's ok to receive an
EOF at any moment. Channels that have some form of strict EOF
tracking, such as TLS session termination, may choose to ignore EOF
errors with the use of this flag.

This is being added for compatibility with older migration streams
that do not include a TLS termination step.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>