kernel: ipv6: mcast: extend RCU protection in igmp6_send()

In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: extend RCU protection in igmp6send igmp6send can be called without RTNL or RCU being held. Extend RCU protection so that we can safely fetch the net pointer and avoid a potential UAF. Note that we no longer can use...