igmp: Namespaceify igmp_llm_reports sysctl knob

This was initially introduced in df2cf4a78e488d26 ("IGMP: Inhibit
reports for local multicast groups") by defining the sysctl in the
ipv4_net_table array, however it was never implemented to be
namespace aware. Fix this by changing the code accordingly.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 522a2cf..cbbf811 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -110,6 +110,7 @@
 
 	int sysctl_igmp_max_memberships;
 	int sysctl_igmp_max_msf;
+	int sysctl_igmp_llm_reports;
 
 	struct ping_group_range ping_group_range;