crash fix: ctl->iiwidth_len was not initialized correctly

crash fix: ctl->iiwidth_len was not initialized correctly

It was a mistake to add iiwidth_len to struct mtr_ctl.  First of all the
value needed in that field was never set, and that resulted to crash when
running command with --csv option.

Secondly adding the field was bad idea to begin with.  Number of array
elements is known only within context of asn.c file, so it is better to add
interface to query it rather than try to set value to a structure.  Later
design is prone to cause futher bugs, if/when execution flow is not as one
might assume.