Best Effort User Input Validation Checks

[kb1lqc]

Pulling in #30 for best effort user input validation.

• Checks all current user input options for valid types and values where applicable
• Some checks are not easy/possible at this time such as timeout being a NoneType due to default argparse values.
• No unit testing of the values yet but manual testing performed
• mtu size set to RFC 791 min/max
• callsign set to min of 3 characters and max of 7 characters
• Updated argparse types where applicable