Handle unknown codecs sent by HF

Use case:
1. Connect to headset supporting CVSD, mSBC and other codecs.
2. Verify if headset sending AT+BAC with supported codecs.
3. Check if SCO is established with mSBC codec.

Failure:
SCO is established with CVSD codec.

Root cause:
When parsing AT+BAC command, if unknown codec is received,
we are falling back to CVSD although mSBC is supported in HF.

Fix:
AT+BAC parsing function modified to return correct codecs
supported by HF when it encounters unknown codecs in arguments
of AT+BAC.

Change-Id: I9ac7675c9d863e7362f85e3b7b8d9a42462bd5e9