scd: Fix receive buffer size.

* scd/apdu.c (send_le): Fix the size, adding two for status
bytes to Le.

Backport of master commit: 5c2db9dedfe9dbb14ffec24751ca23a69cead94e

This is long standing bug. So far, Le was not exact value.
Since forthcoming change will introduce exact value of expected length
of response data, this change is needed.

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>