Increase default SASL buffer size

Default SASL buffer size was too small and could lead for example to
migration errors.

https://fedorahosted.org/freeipa/ticket/3826

install/updates/10-config.update

@@ -57,3 +57,9 @@ addifnew:nsSaslMapPriority: 10
 
 dn: cn=Name Only,cn=mapping,cn=sasl,cn=config
 addifnew:nsSaslMapPriority: 10
+
+# Default SASL buffer size was too small and could lead for example to
+# migration errors
+# Can be removed when https://fedorahosted.org/389/ticket/47457 is fixed
+dn: cn=config
+only:nsslapd-sasl-max-buffer-size:2097152