Bug#780980: logs with error severity when TLS shutdown cleanly by peer

[Daniel Pocock]

Package: resiprocate
Version: 1.9.7-4
Severity: important

If a TLS connection is shutdown cleanly by the peer,
SSL_ERROR_ZERO_RETURN is logged with the severity of other types of
error when it is not really an error.  This is unhelpful and confusing
when troubleshooting as well as making excessive log alerts for people
who monitor the logs closely.

This is already fixed upstream on the master branch.