backend-native: Fix stack corruption reading RFCOMM AT+BIA= response
On-stack buffer size is too short for sscanf to read AT+BIA= and AT+BAC= response strings which have variable length. Fix this by replacing sscanf with proper copy of input string. Fixes: cca0d693 ("bluetooth: add AT+BIA support") Part-of: <pulseaudio/pulseaudio!755>