Floss: check |wbs_supported| in AT+BAC

Some boards don't support WBS, and the stack may store that value as a
result of codec negotiation.

In the end it likely does no harm as of now, since in
|bta_ag_create_sco| there is another check.

This CL ensures the unsupported codec would not be kept to be safe.

Bug: 306067195
Tag: #floss
Test: atest net_test_stack_btm
Change-Id: I40ad7cd05ac7f552b497a361ca8190f075d92a1b