MEDIUM: ssl: ssl-load-extra-del-ext work only with .crt

In order to be compatible with the "set ssl cert" command of the CLI,
this patch restrict the ssl-load-extra-del-ext to files with a ".crt"
extension in the configuration.

Related to issue #785.

Should be backported where 8e8581e ("MINOR: ssl: 'ssl-load-extra-del-ext'
removes the certificate extension") was backported.
2 files changed