[NET]: docbook fixes for netif_ functions

Documentation updates for network interfaces.

1. Add doc for netif_napi_add
2. Remove doc for unused returns from netif_rx
3. Add doc for netif_receive_skb

[ Incorporated minor mods from Randy Dunlap -DaveM ]

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1751,9 +1751,6 @@ DEFINE_PER_CPU(struct netif_rx_stats, netdev_rx_stat) = { 0, };
  *
  *	return values:
  *	NET_RX_SUCCESS	(no congestion)
- *	NET_RX_CN_LOW   (low congestion)
- *	NET_RX_CN_MOD   (moderate congestion)
- *	NET_RX_CN_HIGH  (high congestion)
  *	NET_RX_DROP     (packet was dropped)
  *
  */
@@ -2001,6 +1998,21 @@ out:
 }
 #endif
 
+/**
+ *	netif_receive_skb - process receive buffer from network
+ *	@skb: buffer to process
+ *
+ *	netif_receive_skb() is the main receive data processing function.
+ *	It always succeeds. The buffer may be dropped during processing
+ *	for congestion control or by the protocol layers.
+ *
+ *	This function may only be called from softirq context and interrupts
+ *	should be enabled.
+ *
+ *	Return values (usually ignored):
+ *	NET_RX_SUCCESS: no congestion
+ *	NET_RX_DROP: packet was dropped
+ */
 int netif_receive_skb(struct sk_buff *skb)
 {
 	struct packet_type *ptype, *pt_prev;