ssh: T8090: add support for config test mode (sshd -t)

Add a safety-net for development to check if the rendered sshd(8) configuration
can be applied at all. If it can't be applied - throw an error.

From https://linux.die.net/man/8/sshd:
  -t    Test mode. Only check the validity of the configuration file and sanity
        of the keys. This is useful for updating sshd reliably as configuration
        options may change.

Explicitly forcing a broken config now results in:

  vyos@vyos# commit
  [ service ssh ]
  Unexpected error with SSH configuration! /run/sshd/sshd_config line 21:
  X11DisplayOffset integer value invalid.
  [[service ssh]] failed
  Commit failed

0 files changed, 0 insertions, 0 deletions