ipv6: Set cfg.ifa_flags before device lookup in inet6_rtm_newaddr().

We will convert inet6_rtm_newaddr() to per-netns RTNL.

Except for IFA_F_OPTIMISTIC, cfg.ifa_flags can be set before
__dev_get_by_index().

Let's move ifa_flags setup before __dev_get_by_index() so that
we can set ifa_flags without RTNL.

Also, now it's moved before tb[IFA_CACHEINFO] in preparing for
the next patch.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115080608.28127-9-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: q2ven

net/ipv6/addrconf.c

@@ -5021,6 +5021,13 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (tb[IFA_PROTO])
 		cfg.ifa_proto = nla_get_u8(tb[IFA_PROTO]);
 
+	cfg.ifa_flags = nla_get_u32_default(tb[IFA_FLAGS], ifm->ifa_flags);
+
+	/* We ignore other flags so far. */
+	cfg.ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS |
+			 IFA_F_MANAGETEMPADDR | IFA_F_NOPREFIXROUTE |
+			 IFA_F_MCAUTOJOIN | IFA_F_OPTIMISTIC;
+
 	cfg.valid_lft = INFINITY_LIFE_TIME;
 	cfg.preferred_lft = INFINITY_LIFE_TIME;
 
@@ -5038,13 +5045,6 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 		return -ENODEV;
 	}
 
-	cfg.ifa_flags = nla_get_u32_default(tb[IFA_FLAGS], ifm->ifa_flags);
-
-	/* We ignore other flags so far. */
-	cfg.ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS |
-			 IFA_F_MANAGETEMPADDR | IFA_F_NOPREFIXROUTE |
-			 IFA_F_MCAUTOJOIN | IFA_F_OPTIMISTIC;
-
 	idev = ipv6_find_idev(dev);
 	if (IS_ERR(idev))
 		return PTR_ERR(idev);