A2DP: More clear log messages for both BTA and AVDT SCB handle

There were 2 types of handles for the stream control mapping between BTA
and AVDT, tBTA_AV_HNDL and for AvdtpScb respectively, and the stack used
them to communicate crossing layers. However, both of them were all
named *handle* in logs, and was not easy to read. This CL uses
bta_handle / bta_av_handle for tBTA_AV_HNDL and avdt_handle for
AvdtpScb, and raise the log level to be error if AVDT API failed.

Bug: 135655859
Bug: 145326274
Test: Logs changed only. Disconnecting / Reconnecting by A2DP manually
Change-Id: I780561ff4fbd3be0ed54376346fbdad3efb845ed