gtp: add missing gtp_encap_disable_sock() in gtp_encap_enable()

If an invalid role is sent from user space, gtp_encap_enable() will fail.
Then, it should call gtp_encap_disable_sock() but current code doesn't.
It makes memory leak.

Fixes: 91ed81f9 ("gtp: support SGSN-side tunnels")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/gtp.c

@@ -857,8 +857,13 @@ static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[])
 
 	if (data[IFLA_GTP_ROLE]) {
 		role = nla_get_u32(data[IFLA_GTP_ROLE]);
-		if (role > GTP_ROLE_SGSN)
+		if (role > GTP_ROLE_SGSN) {
+			if (sk0)
+				gtp_encap_disable_sock(sk0);
+			if (sk1u)
+				gtp_encap_disable_sock(sk1u);
 			return -EINVAL;
+		}
 	}
 
 	gtp->sk0 = sk0;