package/openldap: security bump to version 2.4.48

Security fixes:
CVE-2019-13057: Fixed slapd to restrict rootDN proxyauthz to its own databases
CVE-2019-13565: Fixed slapd to initialize SASL SSF per connection

Full changelog:
https://www.openldap.org/lists/openldap-announce/201907/msg00001.html



Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
[Peter: fix sha256 hash line]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>