docs: netdev: reshuffle sections in prep for de-FAQization

Subsequent changes will reformat the doc away from FAQ.
To make that more readable perform the pure section moves now.
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>