--latestv4 is (no-longer) broken but directory is deprecated

[mzpqnxow]

Hello - thanks for maintaining this project, it's really useful for me

Main Issue(s)

First, FTP downloads are were broken, so pyasn_util_download.py --latestv4 is was failing yesterday when I used the tool manually for the first time in a while. I'm not sure for how long that was the case. See:

routeviews/issues#263

The routeviews project was kind enough to resolve the issue yesterday on their side. I had considered sending a PR to pyasn, to change bgpdata to route-views2/bgpdata, but then decided to send an issue there to see if it could be fixed at the root, and get some clarification as to whether it was intended, So it is now working again.

More important, though, they also posted this clarifying the use of that directory. They're suggesting /bgpdata not be used at all. Assuming you'd like to accept a change for this, I can send a PR. It's very simple:

the function find_latest_routeviews changes very slightly. The original:

pyasn/pyasn-utils/pyasn_util_download.py

Lines 110 to 119 in 4aa80e9

	def find_latest_routeviews(archive_ipv):
	# RouteViews archives are as follows:
	# ftp://archive.routeviews.org/datapath/YYYYMM/ribs/XXXX
	archive_ipv = str(archive_ipv)
	assert archive_ipv in ('4', '6', '46', '64')
	return find_latest_in_ftp(server='archive.routeviews.org',
	archive_root='bgpdata' if archive_ipv == '4' else
	'route-views6/bgpdata' if archive_ipv == '6' else
	'route-views4/bgpdata', # 4+6
	sub_dir='RIBS')

The first case in the archive_root kwarg will go from bgpdata to route-views2/bgpdata

Making this change isn't necessarily required - nothing is broken at this current point in time; it is also not guaranteed to become broken. But it might become broken, at some point, based on my understanding of the statement I linked above.

I'll be entering a separate issue later on that is somewhat related (but very different) that is also about pyasn_util_download.py, but about enhancements (not changing the default behavior further, though - just opt-in enhancements)

Thanks again for your work, I know maintaining a project like this is often a thankless task, and time is rarely plentiful