Fix how RawAddress is created for btif API in the HFP facade service.

Since `from_bytes` expects a 6 bytes input while we encode the string representation directly, they aren't exactly the same.
Since RawAddress implements the address generation logic from string, it is easier to directly use it instead of implementing it on our own on the tests.

Bug: 250899887
Test: system/gd/cert/run --topshim --clean
Tag: #floss
Change-Id: I3747a13508a7b367d5a83a164963af415a5ad870