SAP: Fix ANR(s) in SAP server code

Fix ANR in SAP Server code in following scenarios:

  - Multiple call to stop in Sapservice leads to ANR, as check was not
    present in stop to prevent unregistering BroadcastReceiver if not
    already registred.
  - Remove redundant call to closeServerSocket from initSocket as this could
    lead to ANR when there is simultaneous call to closeService as part of BT
    being switched off and call to start SAP as part of BT being turned on when
    BT on off sequence is tried repeatedly.

Change-Id: Ia6bc5ca7c9da9ae4a4c12e8207fb9ff6b9159e82