Replace HTTP links with HTTPS ones: 9P FILE SYSTEM

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.
Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200708145804.14887-1-grandmaster@al2klimov.deSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/9p.rst

@@ -18,7 +18,7 @@ and Maya Gokhale.  Additional development by Greg Watson
 The best detailed explanation of the Linux implementation and applications of
 the 9p client is available in the form of a USENIX paper:
 
-   http://www.usenix.org/events/usenix05/tech/freenix/hensbergen.html
+   https://www.usenix.org/events/usenix05/tech/freenix/hensbergen.html
 
 Other applications are described in the following papers: