af_unix: introduce unix_skb_to_scm helper

Instead of open-coding let's consolidate this logic in a separate
helper. This will simplify further changes.

Cc: [e-mail]
Cc: [e-mail]
Cc: David S. Miller <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: Paolo Abeni <[e-mail]>
Cc: Simon Horman <[e-mail]>
Cc: Leon Romanovsky <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Kuniyuki Iwashima <[e-mail]>
Cc: Lennart Poettering <[e-mail]>
Cc: Luca Boccassi <[e-mail]>
Cc: David Rheinsberg <[e-mail]>
Signed-off-by: Alexander Mikhalitsyn <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Christian Brauner <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

net/unix/af_unix.c

···
 	return err;
 }
 
+static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
+{
+	scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
+	unix_set_secdata(scm, skb);
+}
+
 /**
  * unix_maybe_add_creds() - Adds current task uid/gid and struct pid to skb if needed.
  * @skb: skb to attach creds to.
···
 
 	memset(&scm, 0, sizeof(scm));
 
-	scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
-	unix_set_secdata(&scm, skb);
+	unix_skb_to_scm(skb, &scm);
 
 	if (!(flags & MSG_PEEK)) {
 		if (UNIXCB(skb).fp)
···
 				break;
 		} else if (unix_may_passcred(sk)) {
 			/* Copy credentials */
-			scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
-			unix_set_secdata(&scm, skb);
+			unix_skb_to_scm(skb, &scm);
 			check_creds = true;
 		}