net: l2tp: unlock socket lock before returning from l2tp_ip_sendmsg

l2tp_ip_sendmsg could return without releasing socket lock, making it all the
way to userspace, and generating the following warning:

[  130.891594] ================================================
[  130.894569] [ BUG: lock held when returning to user space! ]
[  130.897257] 3.4.0-rc5-next-20120501-sasha #104 Tainted: G        W
[  130.900336] ------------------------------------------------
[  130.902996] trinity/8384 is leaving the kernel with locks still held!
[  130.906106] 1 lock held by trinity/8384:
[  130.907924]  #0:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff82b9503f>] l2tp_ip_sendmsg+0x2f/0x550

Introduced by commit 2f16270f ("l2tp: Fix locking in l2tp_ip.c").
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip.c

@@ -442,8 +442,9 @@ static int l2tp_ip_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *m
 
 		daddr = lip->l2tp_addr.s_addr;
 	} else {
+		rc = -EDESTADDRREQ;
 		if (sk->sk_state != TCP_ESTABLISHED)
-			return -EDESTADDRREQ;
+			goto out;
 
 		daddr = inet->inet_daddr;
 		connected = 1;