IsoManager: Add additional statistics

This adds additional statistics of the ongoing ISO data traffic
in the following form:
       Credits Stats:
          Credits underflow (count): 3637
          Credits underflow (bytes): 218220
          Last underflow time ago (ms): 78
        Event Stats:
          Sequence number mismatch (count): 0
          Event lost (count): 0
          Last event lost time ago (ms): 0

Bug: 150670922
Tag: #feature
Test: build, flash and manually tested
Sponsor: jpawlowski@
Change-Id: I4071eb9f5c4495ad98003c4c931e6a68de393b91