BluetoothMetrics: Rename KEY_UNKNOWN to COUNTER_KEY_UNKNOWN

KEY_UNKNOWN might clash with linux's input-event-codes.h.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/input-event-codes.h#n324
It doesn't seem to be used though so we can just rename it here.

Bug: 291522341
Test: m -j
Change-Id: I5d32a66ae5ad461279c2f137b5d4edd6e3168f47
1 file changed
tree: 3a401002e10d88093e8c7d1a14645ae8201a9314
  1. stats/
  2. OWNERS