Fix a race condition in the A2dpProfile constructor

When constructing A2dpProfile objects, we were creating an
A2dpServiceListener before initializing the mWrapperFactory instance
variable that it depended on. If the onServiceConnected callback happens
immediately after the listener is created, we'd get a null pointer
exception. The fix is to move initialization of mWrapperFactory up before
the construction of the A2dpServiceListener.

Bug: 38391718
Test: run boot tests
Change-Id: Ib0be947099862b19da7737b54b99b944241b605f