Configure sshnpd from a file

[cpswan]

Is your feature request related to a problem? Please describe.

When running the daemon as a service it's customary to have a config file rather than passing a multitude of command line options (that then have to be configured into an init script, systemd unit etc.)

Describe the solution you'd like

Starting the the C daemon

• Have a default config location (e.g. /etc/sshnpd.conf)
• Test for the presence of the config file (and suitable config within it) before parsing command line args
• Allow config in the file to be overridden by command line args
• Allow for the file to be located elsewhere and specified with a command line arg

Describe alternatives you've considered

Windows registry (later)

[cpswan]

@XavierChanth having worked some more on the packaging of config and init for OpenWRT I don't think this is on the critical path (or even necessary) for that, so maybe we can deprioritise?

[XavierChanth]

Changed to P3 & backlogged it.