quota: Fixup http links in quota doc

Switch link to Sourceforge in quota documentation to https and replace
link for libnl documentation with a working one from infradead.

Signed-off-by: Jan Kara <jack@suse.cz>

Replace HTTP links with HTTPS ones: DISKQUOTA

Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
If not .svg:
For each line:
If doesn't contain `\bxmlns\b`:
For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
If both the HTTP and HTTPS versions
return 200 OK and serve the same content:
Replace HTTP with HTTPS.

Link: https://lore.kernel.org/r/20200708171905.15396-1-grandmaster@al2klimov.de
Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Signed-off-by: Jan Kara <jack@suse.cz>

docs: filesystems: convert quota.txt to ReST

- Add a SPDX header;
- Adjust document title;
- Some whitespace fixes and new line breaks;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/10a707377475bb252f454af2b8f58a038527933f.1588021877.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>