net: igmp: Don't flush routing cache when force_igmp_version is modified

The procfs knob /proc/sys/net/ipv4/conf/*/force_igmp_version allows the
IGMP protocol version to use to be explicitly set.  As a side effect this
caused the routing cache to be flushed as it was declared as a
DEVINET_SYSCTL_FLUSHING_ENTRY.  Flushing is unnecessary and this patch
makes it so flushing does not occur.

Requested by Hannes Frederic Sowa as he was reviewing other patches
adding procfs entries.
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: William Manley <william.manley@youview.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/inetdevice.h

@@ -27,9 +27,9 @@ enum
 	IPV4_DEVCONF_TAG,
 	IPV4_DEVCONF_ARPFILTER,
 	IPV4_DEVCONF_MEDIUM_ID,
+	IPV4_DEVCONF_FORCE_IGMP_VERSION,
 	IPV4_DEVCONF_NOXFRM,
 	IPV4_DEVCONF_NOPOLICY,
-	IPV4_DEVCONF_FORCE_IGMP_VERSION,
 	IPV4_DEVCONF_ARP_ANNOUNCE,
 	IPV4_DEVCONF_ARP_IGNORE,
 	IPV4_DEVCONF_PROMOTE_SECONDARIES,

net/ipv4/devinet.c

@@ -2094,11 +2094,11 @@ static struct devinet_sysctl_table {
 		DEVINET_SYSCTL_RW_ENTRY(ARP_ACCEPT, "arp_accept"),
 		DEVINET_SYSCTL_RW_ENTRY(ARP_NOTIFY, "arp_notify"),
 		DEVINET_SYSCTL_RW_ENTRY(PROXY_ARP_PVLAN, "proxy_arp_pvlan"),
+		DEVINET_SYSCTL_RW_ENTRY(FORCE_IGMP_VERSION,
+					"force_igmp_version"),
 
 		DEVINET_SYSCTL_FLUSHING_ENTRY(NOXFRM, "disable_xfrm"),
 		DEVINET_SYSCTL_FLUSHING_ENTRY(NOPOLICY, "disable_policy"),
-		DEVINET_SYSCTL_FLUSHING_ENTRY(FORCE_IGMP_VERSION,
-					      "force_igmp_version"),
 		DEVINET_SYSCTL_FLUSHING_ENTRY(PROMOTE_SECONDARIES,
 					      "promote_secondaries"),
 		DEVINET_SYSCTL_FLUSHING_ENTRY(ROUTE_LOCALNET,