checkpatch: check for misuse of the link tags

"Link:" and "Closes:" tags have to be used with public URLs.

It is difficult to make sure the link is public but at least we can verify
the tag is followed by 'http(s)://'.

With that, we avoid such a tag that is not allowed [1]:

  Closes: <number>

Now that we check the "link" tags are followed by a URL, we can relax the
check linked to "Reported-by being followed by a link tag" to only verify
if a "link" tag is present after the "Reported-by" one.

Link: https://lore.kernel.org/linux-doc/CAHk-=wh0v1EeDV3v8TzK81nDC40=XuTdY2MCr0xy3m3FiBV3+Q@mail.gmail.com/ [1]
Link: https://lkml.kernel.org/r/20230314-doc-checkpatch-closes-tag-v4-5-d26d1fa66f9f@tessares.net


Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Acked-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kai Wasserbäch <kai@dev.carbon-project.org>
Cc: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>