Fix ANR by repeating BT ON/OFF caused by PBAP closeservice deadlock

Move back socket closing sequence ahead of Thread.shutdown and join operation;
Seperate socket closing and resetting as null to avoid NPE during service close

Original Author: Fan Jackson
Bug: 2158262
DrNo: Paul

Change-Id: I2b36f3fb920c80602f5734a67a8cf6c6fbd00de4