kernel: describe bridge patch "multicast to unicast"

It was initially added in r41367 by nbd.

SVN-Revision: 46828

target/linux/generic/patches-3.18/645-bridge_multicast_to_unicast.patch

+From: Felix Fietkau <nbd@openwrt.org>
+Subject: [PATCH] bridge: multicast to unicast
+
+Implement optinal multicast->unicast conversion for igmp snooping
+---
 --- a/net/bridge/br_multicast.c
 +++ b/net/bridge/br_multicast.c
 @@ -635,7 +635,8 @@ struct net_bridge_port_group *br_multica

target/linux/generic/patches-4.0/645-bridge_multicast_to_unicast.patch

+From: Felix Fietkau <nbd@openwrt.org>
+Subject: [PATCH] bridge: multicast to unicast
+
+Implement optinal multicast->unicast conversion for igmp snooping
+---
 --- a/include/linux/if_bridge.h
 +++ b/include/linux/if_bridge.h
 @@ -45,6 +45,7 @@ struct br_ip_list {

target/linux/generic/patches-4.1/645-bridge_multicast_to_unicast.patch

+From: Felix Fietkau <nbd@openwrt.org>
+Subject: [PATCH] bridge: multicast to unicast
+
+Implement optinal multicast->unicast conversion for igmp snooping
+---
 --- a/include/linux/if_bridge.h
 +++ b/include/linux/if_bridge.h
 @@ -46,6 +46,7 @@ struct br_ip_list {