genetlink: fix genl_bind() invoking bind() after -EPERM

In the Linux kernel, the following vulnerability has been resolved:

genetlink: fix genl_bind() invoking bind() after -EPERM

Per family bind/unbind callbacks were introduced to allow families to track multicast group consumer presence, e.g. to start or stop producing events depending on listeners.

However, in genl_bind() the bind() callback was invoked even if capability checks failed and ret was set to -EPERM. This means that callbacks could run on behalf of unauthorized callers while the syscall still returned failure to user space.

Fix this by only invoking bind() after "if (ret) break;" check i.e. after permission checks have succeeded.