wifi: iwlwifi: fix potential use after free in iwl_mld_remove_link()

In the Linux kernel, the following vulnerability has been resolved: wifi: iwlwifi: fix potential use after free in iwl_mld_remove_link() This code frees "link" by calling kfree_rcu(link, rcu_head) and then it dereferences "link" to get the "link->fw_id". Save the "link->fw_id" first to avoid a potential use after free.