wpa_supplicant(hidl): Fix pin string generation

Moved all of these conversions to a utility in misc_utils. The previous
conversion method was not modifying the string.size() param and hence
the written string was lost.

Bug: 34714021
Test: Able to initiate WPS display requests from framework now.
Change-Id: Id4d48010402c13d9d78ef5d209dbbaff7a80f954
4 files changed