Bluetooth: fix oops in l2cap_connect_req

In error cases when the ACL is insecure or we fail to allocate a new
struct sock, we jump to the "response" label.  If so, "sk" will be
null and the kernel crashes.

Signed-off-by: Nathan Holstein <nathan.holstein@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>