murmur_git: mark as not broken without iceSupport

pkgs/applications/networking/mumble/default.nix

···
   mumble_git = client gitSource;
   murmur     = server stableSource;
   murmur_git = (server gitSource).overrideAttrs (old: {
-    meta = old.meta // { broken = true; };
+    meta = old.meta // { broken = iceSupport; };
   });
 }

pkgs/top-level/all-packages.nix

···
       speechdSupport = config.mumble.speechdSupport or false;
       pulseSupport = config.pulseaudio or false;
       iceSupport = config.murmur.iceSupport or true;
-    }) mumble mumble_git murmur murmur_git;
+    }) mumble mumble_git murmur;
+
+  inherit (callPackages ../applications/networking/mumble {
+      avahi = avahi.override {
+        withLibdnssdCompat = true;
+      };
+      qt5 = qt56; # Mumble doesn't work with Qt > 5.5
+      jackSupport = config.mumble.jackSupport or false;
+      speechdSupport = config.mumble.speechdSupport or false;
+      pulseSupport = config.pulseaudio or false;
+      iceSupport = false;
+    }) murmur_git;
 
   mumble_overlay = callPackage ../applications/networking/mumble/overlay.nix {
     mumble_i686 = if system == "x86_64-linux"