From Stephen Donnelly:

From Stephen Donnelly:

	If the DAG API supports asking a card for the set of ERF types
	it supports, use that capability, to handle cards that support
	multiple ERF types.  This is to support channelised/fractional
	T1/E1.

	Don't set the snapshot length - some DAG cards support multiple
	capture streams, but the snapshot length is global, so it'd
	affect other captures.

	Update README.dag.