Ignore AAC bitrate from the A2DP Sink device if below a threshold

Some Sink devices might advertise AAC zero bitrate or a very small
value (e.g., 24576). Ignore values that are below a threshold
(currently set to 64000), because those seem invalid.
For such devices, the actual streaming bitrate will be computed
based on the MTU.

Test: Code compilation
Change-Id: Ibe3de6e53681a618f388b41a01f366ad462b7a1d