BT: Using ConcurrentHashMap for connection list

- Bluetooth Off operation during active Browse
  connection causes concurrent access of conn
  map with cleanup and other browse related
  operations.
- This change updates datatype of conn list map
  to ConcurrentHashMap to accommodate such
  scenarios.

CRs-Fixed: 2557454

Change-Id: I2208cb817a04403a96055f55a88963dd0c9402c2
1 file changed