docs: networking: reorganize driver documentation again

Organize driver documentation by device type. Most documents
have fairly verbose yet uninformative names, so let users
first select a well defined device type, and then search for
a particular driver.

While at it rename the section from Vendor drivers to
Hardware drivers. This seems more accurate, besides people
sometimes refer to out-of-tree drivers as vendor drivers.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/device_drivers/ethernet/index.rst

+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+
+Ethernet Device Drivers
+=======================
+
+Device drivers for Ethernet and Ethernet-based virtual function devices.
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   3com/3c509
+   3com/vortex
+   amazon/ena
+   aquantia/atlantic
+   chelsio/cxgb
+   cirrus/cs89x0
+   dlink/dl2k
+   davicom/dm9000
+   dec/de4x5
+   dec/dmfe
+   freescale/dpaa
+   freescale/dpaa2/index
+   freescale/gianfar
+   google/gve
+   intel/e100
+   intel/e1000
+   intel/e1000e
+   intel/fm10k
+   intel/igb
+   intel/igbvf
+   intel/ixgb
+   intel/ixgbe
+   intel/ixgbevf
+   intel/i40e
+   intel/iavf
+   intel/ice
+   marvell/octeontx2
+   mellanox/mlx5
+   microsoft/netvsc
+   neterion/s2io
+   neterion/vxge
+   netronome/nfp
+   pensando/ionic
+   smsc/smc9
+   stmicro/stmmac
+   ti/cpsw
+   ti/cpsw_switchdev
+   ti/tlan
+   toshiba/spider_net
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`