igmp: Document sysctl_igmp_max_msf

Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -946,6 +946,11 @@ igmp_max_memberships - INTEGER
 	The value 5459 assumes no IP header options, so in practice
 	this number may be lower.
 
+igmp_max_msf - INTEGER
+	Maximum number of addresses allowed in the source filter list for a
+	multicast group.
+	Default: 10
+
 igmp_qrv - INTEGER
 	Controls the IGMP query robustness variable (see RFC2236 8.1).
 	Default: 2 (as specified by RFC2236 8.1)