Bluetooth: Fix RfComm socket cursor exceptions in STRICT MODE.

Perform ParcelFileDescriptor close after detach to avoid bluetooth
socket leaks in strict mode.

CRs-fixed: 572214

Change-Id: Ib0d7d08e17aa147573e9893af9b605fd42420500
connectivity: allow inheritance to subclass

set modifier to protected in order to allow
subclass to use the same data and avoid redefinition.

Change-Id: I2dc688d3e433775cb073ec6faae3981807212cc9