samba: readd liburing to buildInputs on Linux

ce5ebeb90c ("samba4: fixup build on linux") removed liburing from
buildInputs on Linux to work around a compilation error [1]. A fix for
the compilation error was included in liburing 2.11 [2]. Readd the
liburing dependency to restore support for vfs_io_uring.

[1]: https://hydra.nixos.org/build/298833701/nixlog/3/tail
[2]: https://github.com/axboe/liburing/commit/1b99ce4856f64c1056b3c394062cba35bd045718

pkgs/servers/samba/4.x.nix

@@ -167,7 +167,7 @@ stdenv.mkDerivation (finalAttrs: {
       libbsd
     ]
     ++ optionals stdenv.hostPlatform.isLinux [
-      #liburing # FIXME: better solution
+      liburing
       systemd
     ]
     ++ optionals stdenv.hostPlatform.isDarwin [ libiconv ]