Bluetooth socket constants missing on Linux

[dlech]

#13044 disabled Bluetooth-related socket constants like AF_BLUETOOTH on Linux. However, these constants are available on Linux (assuming bluetooth/bluetooth.h was present when Python was built).

[tungol]

Sorry about that! The bluetooth constants aren't present in the Linux version of the Github Actions pipeline, which is what that MR used to judge what was on Linux or not. I've put up an MR that restores the constants on Linux.