docs: process/howto.rst: make sections on bug reporting match practice

The file Documentation/process/howto.rst points to bugzilla.kernel.org
as the primary place to report kernel bugs to. For most of the kernel
that's the wrong place, as the MAINTAINERS file shows. Adjust those
sections to make them match current practice.

This change also removes a contradiction with the recently added text
Documentation/admin-guide/reporting-issues.rst, which is a reason for a
'this needs further discussion' warning note in there. The change is
thus a prerequisite to remove that warning, nevertheless it is left for
now to make sure people review the text's approach more carefully.

Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210116143542.69199-1-linux@leemhuis.info


Signed-off-by: Jonathan Corbet <corbet@lwn.net>