Update Android Headtracker data size

Headtracker report should only be 13 bytes but we allocate 15 bytes in the
CIS. This means that we are wasting 2 bytes worth of bandwidth per CIS
subevent.

Test: mmm packages/modules/Bluetooth
Flag: com.android.bluetooth.flags.headtracker_sdu_size
Bug: 349901879
Bug: 350090733
Change-Id: I4e1bf8fb588065bb8d2360d487f365a94fcad69d