Gateway Monitor Advanced Settings

Exposes 3 additional apinger configuration options in the gateway monitor advanced section which can either be set manually, calculated based on interval, or use the hard coded defaults.
	1) Avg Delay Samples
	2) Avg Loss Samples
	3) Avg Loss Delay Samples

The current hard coded defaults are okay for a short interval such as the 1 second default.  But do not work well when a longer interval is required.
Gateway Monitor Advanced Settings

Recommended changes made to calculated value input behavior.
Restrict interval to integer of 1 or greater.
Merge pull request #890 from N0YB/Gateway_Monitor

Gateway Monitor Advanced Settings