[Filebeat] Netflow input - convert to input API v2

[andrewkroh]

Describe the enhancement:

The netflow input should be converted to the v2 API in order to take advantage of the ability to control beat.Client configuration.

The "v2" API is defined at. The netflow input itself is a stateless (has no persistant state to store in a "cursor").

beats/filebeat/input/v2/input.go

Lines 58 to 76 in 64460ba

	// Input is a configured input object that can be used to test or start
	// the actual data collection.
	type Input interface {
	// Name reports the input name.
	//
	// XXX: check if/how we can remove this method. Currently it is required for
	// compatibility reasons with existing interfaces in libbeat, autodiscovery
	// and filebeat.
	Name() string
	// Test checks the configuration and runs additional checks if the Input can
	// actually collect data for the given configuration (e.g. check if host/port or files are
	// accessible).
	Test(TestContext) error
	// Run starts the data collection. Run must return an error only if the
	// error is fatal making it impossible for the input to recover.
	Run(Context, beat.PipelineConnector) error
	}

[elasticmachine]

Pinging @elastic/sec-deployment-and-devices (Team:Security-Deployment and Devices)