isdnloop: use strlcpy() instead of strcpy()

[ Upstream commit f9a23c84 ]

These strings come from a copy_from_user() and there is no way to be
sure they are NUL terminated.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>