ipv6: mcast: Remove unnecessary ASSERT_RTNL and comment.

JIRA: https://issues.redhat.com/browse/RHEL-115325

commit 49b8223
Author: Kuniyuki Iwashima <kuniyu@google.com>
Date:   Wed Jul 2 16:01:27 2025 -0700

    ipv6: mcast: Remove unnecessary ASSERT_RTNL and comment.

    Now, RTNL is not needed for mcast code, and what's commented in
    ip6_mc_msfget() is apparent by for_each_pmc_socklock(), which has
    lockdep annotation for lock_sock().

    Let's remove the comment and ASSERT_RTNL() in ipv6_mc_rejoin_groups().

    Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://patch.msgid.link/20250702230210.3115355-11-kuni1840@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/ipv6/mcast.c

@@ -605,10 +605,6 @@ int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
 	if (!ipv6_addr_is_multicast(group))
 		return -EINVAL;
 
-	/* changes to the ipv6_mc_list require the socket lock and
-	 * rtnl lock. We have the socket lock, so reading the list is safe.
-	 */
-
 	for_each_pmc_socklock(inet6, sk, pmc) {
 		if (pmc->ifindex != gsf->gf_interface)
 			continue;
@@ -2880,8 +2876,6 @@ static void ipv6_mc_rejoin_groups(struct inet6_dev *idev)
 {
 	struct ifmcaddr6 *pmc;
 
-	ASSERT_RTNL();
-
 	mutex_lock(&idev->mc_lock);
 	if (mld_in_v1_mode(idev)) {
 		for_each_mc_mclock(idev, pmc)