mptcp: move sk assignment statement ahead

If we move the sk assignment statement ahead in mptcp_nl_cmd_sf_create()
or mptcp_nl_cmd_sf_destroy(), right after the msk null-check statements,
sk can be used after the create_err or destroy_err labels instead of
open-coding it again.

Reviewed-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231025-send-net-next-20231025-v1-7-db8f25f798eb@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: geliangtang

net/mptcp/pm_userspace.c

@@ -335,6 +335,8 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 		return err;
 	}
 
+	sk = (struct sock *)msk;
+
 	if (!mptcp_pm_is_userspace(msk)) {
 		GENL_SET_ERR_MSG(info, "invalid request; userspace PM not selected");
 		goto create_err;
@@ -352,8 +354,6 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 		goto create_err;
 	}
 
-	sk = (struct sock *)msk;
-
 	if (!mptcp_pm_addr_families_match(sk, &addr_l, &addr_r)) {
 		GENL_SET_ERR_MSG(info, "families mismatch");
 		err = -EINVAL;
@@ -381,7 +381,7 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 	spin_unlock_bh(&msk->pm.lock);
 
  create_err:
-	sock_put((struct sock *)msk);
+	sock_put(sk);
 	return err;
 }
 
@@ -458,6 +458,8 @@ int mptcp_pm_nl_subflow_destroy_doit(struct sk_buff *skb, struct genl_info *info
 		return err;
 	}
 
+	sk = (struct sock *)msk;
+
 	if (!mptcp_pm_is_userspace(msk)) {
 		GENL_SET_ERR_MSG(info, "invalid request; userspace PM not selected");
 		goto destroy_err;
@@ -487,7 +489,6 @@ int mptcp_pm_nl_subflow_destroy_doit(struct sk_buff *skb, struct genl_info *info
 		goto destroy_err;
 	}
 
-	sk = (struct sock *)msk;
 	lock_sock(sk);
 	ssk = mptcp_nl_find_ssk(msk, &addr_l, &addr_r);
 	if (ssk) {
@@ -507,7 +508,7 @@ int mptcp_pm_nl_subflow_destroy_doit(struct sk_buff *skb, struct genl_info *info
 	release_sock(sk);
 
 destroy_err:
-	sock_put((struct sock *)msk);
+	sock_put(sk);
 	return err;
 }