Merge branch 'net-store-netdevs-in-an-xarray'

Jakub Kicinski says:

====================
net: store netdevs in an xarray

One of more annoying developer experience gaps we have in netlink
is iterating over netdevs. It's painful. Add an xarray to make
it trivial.

v1: https://lore.kernel.org/all/20230722014237.4078962-1-kuba@kernel.org/
====================

Link: https://lore.kernel.org/r/20230726185530.2247698-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>