a2dp_vendor_aptx_linux: Add functions that are accidentally removed

https://r.android.com/3158859 accidentally removed some functions from
a2dp_vendor_aptx_linux.cc but kept in a2dp_vendor_aptx.cc. This causes
Floss build breakage.

Bug: 352202669
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: USE=floss_upstream emerge-guybrush floss
Flag: EXEMPT, Floss-only changes
Change-Id: Ic629286042d85a82af77acb362827d5faed8e4f5