Motivation for this change

Proprietary firmware is required to get the Bluetooth controller chip Realtek RTL8761b to work on Linux. Support was added to Linux in this commit. However, the Linux kernel versions in nixpkgs including this commit (5.9 and 5.10) seem to have another Bluetooth bug that keeps this from being useful.

I backported the commit to Linux 5.4, as the surrounding code was not compatible with directly including the commit. The firmware package is based on an AUR package. I tested this on my NixOS x86_64 system using a USB Bluetooth controller with a RTL8761b chip.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.