l2tp: unmanaged L2TPv3 tunnels fixes

Followup to commit 789a4a2c 
(l2tp: Add support for static unmanaged L2TPv3 tunnels)

One missing init in l2tp_tunnel_sock_create() could access random kernel
memory, and a bit field should be unsigned.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 13ed85b..98dfcce 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1227,7 +1227,7 @@
 	int err = -EINVAL;
 	struct sockaddr_in udp_addr;
 	struct sockaddr_l2tpip ip_addr;
-	struct socket *sock;
+	struct socket *sock = NULL;
 
 	switch (cfg->encap) {
 	case L2TP_ENCAPTYPE_UDP: