Wrong terminal response for proactive command length errors

This fix is at least reported by an internal test suite
written with the 3gpp specification as base, can not
guarantee that it exists "in the wild" however the
specification is clear.

According to 3gpp11.14, chapter 6.10.6 "Length errors",

If the total lengths of the SIMPLE-TLV data objects are not
consistent with the length given in the BER-TLV data object,
then the whole BER-TLV data object shall be rejected. The
result field in the TERMINAL RESPONSE shall have the error
condition "Command data not understood by ME".

Change-Id: I128442ea4755679b0e5524a31c01b3c690e45ab0