changes:
	* added support for check that every mandatory value inside l2vpn vpls
	nlri exists
	* renamed nlri() to pprint() - actually this was a stupid name for
	the function which only purpose was to print line in the logs
	(and __call__ handling)
	* added unittest for l2vpn nlri encoding and decoding against routes
	which were received from juniper (w/ few hacks coz of Juniper's
	label packing handling)