doc/net: Update git https URLs in netdev-FAQ documentation

DaveM's git tree have been moved into a named subdir 'netdev' to deal with
allowing Jakub Kicinski to help co-maintain the trees.

Link: https://www.kernel.org/doc/html/latest/networking/netdev-FAQ.html


Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>