Reduce indicated maximum PIN length to 15 to support more PIN pad readers

Some PIN PAD reader only support a PIN length up to 15 characters (Most notably REINER SCT Cyberjack readers). The SmartCard-HSM support a PIN in the range 6 to 16 characters, however the PIN range indicated to the reader leads to an error returned in pcsc_pin_cmd().

The proposed patch reduces the advertised maximum PIN length to 15, effectively preventing this problem with affected readers. Please note, that the SmartCard-HSM up to version 1.2 allows changing the PIN size only during initialization.