igmp: Fix data-races around sysctligmpllm_reports.
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.14.290 by commit d77969e7d4ccc26bf1f414a39ef35050a83ba6d5, it was introduced in version v4.3 by commit df2cf4a78e488d26728590cb3c6b4fe4c4862c77. For more details please see the references link.