net: Allow setting network interface to use for multicast

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/HOWTO b/HOWTO
index 3791e7d..38eafdd 100644
--- a/HOWTO
+++ b/HOWTO
@@ -1444,6 +1444,10 @@
 [netsplice] port=int
 [net] port=int	The TCP or UDP port to bind to or connect to.
 
+[netsplice] interface=str
+[net] interface=str  The IP address of the network interface used to send or
+		receive UDP multicast
+
 [netsplice] nodelay=bool
 [net] nodelay=bool	Set TCP_NODELAY on TCP connections.