bonding: add documentation for peer_notif_delay

Ability to tweak the interval between peer notifications has been
added in 07a4ddec ("bonding: add an option to specify a delay
between peer notifications") but the documentation was not updated.
Signed-off-by: Vincent Bernat <vincent@bernat.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/bonding.txt

@@ -707,8 +707,8 @@ num_unsol_na
 	failover event.  As soon as the link is up on the new slave
 	(possibly immediately) a peer notification is sent on the
 	bonding device and each VLAN sub-device. This is repeated at
-	each link monitor interval (arp_interval or miimon, whichever
-	is active) if the number is greater than 1.
+	the rate specified by peer_notif_delay if the number is
+	greater than 1.
 
 	The valid range is 0 - 255; the default value is 1.  These options
 	affect only the active-backup mode.  These options were added for
@@ -727,6 +727,16 @@ packets_per_slave
 	The valid range is 0 - 65535; the default value is 1. This option
 	has effect only in balance-rr mode.
 
+peer_notif_delay
+
+        Specify the delay, in milliseconds, between each peer
+        notification (gratuitous ARP and unsolicited IPv6 Neighbor
+        Advertisement) when they are issued after a failover event.
+        This delay should be a multiple of the link monitor interval
+        (arp_interval or miimon, whichever is active). The default
+        value is 0 which means to match the value of the link monitor
+        interval.
+
 primary
 
 	A string (eth0, eth2, etc) specifying which slave is the