Server configuration

[Anderson Sasaki <ansasaki@xxxxxxxxxx>]

Hello all,

I'm currently implementing support to set the server (bind) options through configuration files. The current state can be followed in the PR I've opened in gitlab [0].

During the implementation, I realized some expected behaviors are not clearly defined (or documented), being the main issue related with the precedence of the options. I followed the implementation of the client side (session) options configuration as close as I could.

So the questions are:
 * Currently if one option is set by one configuration file, the next configuration file can't set it again. Is this the expected behavior from the user point of view?
   - note: This is used to not override user options with the global default options. The user options are parsed and then the global options are parsed. The ones set before are kept. In my opinion it would be better to reverse the logic and parse the global options before and override them with the user options as he or she prefers.

 * If the user sets one option manually (through ssh_options_set()), but the option is defined in the global configuration file, the global setting will overwrite the user setting. Is this expected?
   - note: This happens because setting options manually does not set the bool in the session.options_seen table. When the user calls ssh_connect(), the global configuration will be parsed, overwriting the options set manually by the user. In my opinion, the manually set options should be kept.
 
Resuming, the best for me would be:
 - The global configuration is parsed before any other
 - Settings done manually by the user (either by calling ssh_options_set() or ssh_options_parse_config()) take precedence over the global settings, being kept the last set.
 - Global settings done automatically (e.g. the one called in ssh_connect()) don't override manually set options

Other than this, it would be better to be able to define the default location of the global configuration file in build (cmake) time, instead of having it hardcoded.

Thank you,
Anderson

[0] https://gitlab.com/libssh/libssh-mirror/merge_requests/6