docs: net: reformat driver.rst from a list to sections

docs: net: reformat driver.rst from a list to sections

driver.rst had a historical form of list of common problems.
In the age os Sphinx and rendered documentation it's better
to use the more usual title + text format.

This will allow us to render kdoc into the output more naturally.

No changes to the actual text.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>