docs: networking: convert driver.txt to ReST

- add SPDX header;
- add a document title;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/driver.rst

@@ -1,4 +1,8 @@
-Document about softnet driver issues
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Softnet Driver Issues
+=====================
 
 Transmit path guidelines:
 
@@ -8,7 +12,7 @@ Transmit path guidelines:
    transmit function will become busy.
 
    Instead it must maintain the queue properly.  For example,
-   for a driver implementing scatter-gather this means:
+   for a driver implementing scatter-gather this means::
 
 	static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb,
 					       struct net_device *dev)
@@ -38,22 +42,22 @@ Transmit path guidelines:
 		return NETDEV_TX_OK;
 	}
 
-   And then at the end of your TX reclamation event handling:
+   And then at the end of your TX reclamation event handling::
 
 	if (netif_queue_stopped(dp->dev) &&
 	    TX_BUFFS_AVAIL(dp) > (MAX_SKB_FRAGS + 1))
 		netif_wake_queue(dp->dev);
 
-   For a non-scatter-gather supporting card, the three tests simply become:
+   For a non-scatter-gather supporting card, the three tests simply become::
 
 		/* This is a hard error log it. */
 		if (TX_BUFFS_AVAIL(dp) <= 0)
 
-   and:
+   and::
 
 		if (TX_BUFFS_AVAIL(dp) == 0)
 
-   and:
+   and::
 
 	if (netif_queue_stopped(dp->dev) &&
 	    TX_BUFFS_AVAIL(dp) > 0)

Documentation/networking/index.rst

@@ -53,6 +53,7 @@ Contents:
    decnet
    defza
    dns_resolver
+   driver
 
 .. only::  subproject and html