kernel: icmp6: Fix null-ptr-deref of ip6_null_entry->rt6i_idev in icmp6_dev()

In the Linux kernel, the following vulnerability has been resolved: icmp6: Fix null-ptr-deref of ip6nullentry-rt6iidev in icmp6dev. With some IPv6 Ext Hdr RPL, SRv6, etc., we can send a packet that has the link-local address as src and dst IP and will be forwarded to an external IP in the IPv6 Ex...