am b6432ca4: am 960b31e3: Merge "SipService: unset session listener if listener is gone." into gingerbread

Merge commit 'b6432ca4a090c02a07038f926e9e514d8cb1b657'

* commit 'b6432ca4a090c02a07038f926e9e514d8cb1b657':
  SipService: unset session listener if listener is gone.