chore (c sshnpd): consider exiting more often for certain types of errors.

[XavierChanth]

Certain types of failures should be a log error and exit, running out of heap memory being the main one. However, if the program runs out of heap memory, there are a few reasons as to why that could be:

• Too many sessions active
  • Unlikely, as we minimize the amount of memory allocated before executing srv. This pretty much means we only store the arguments required to invoke srv and hold that in memory until it ends. Someone would have to automate this process, to realistically spin up enough sessions. This would likely be due to a bad actor in the event of an already compromised device, which means crashing would only slow down the damage already being done.
  • Another point worth noting, is that since other sessions are external processes, they will not be killed by exiting sshnpd due to memory related issues.
• Other situations which may be potentially unrecoverable.