ipfs: remove executable bit from systemd units

IPFS would complain with warnings like
Configuration file /nix/store/...-ipfs-0.6.0/etc/systemd/system/ipfs.service is marked executable. Please remove executable permission bits. Proceeding anyway.

(cherry picked from commit 1a382e9)

pkgs/applications/networking/ipfs/default.nix

@@ -27,9 +27,9 @@ buildGoModule rec {
   vendorSha256 = null;
 
   postInstall = ''
-    install -D misc/systemd/ipfs.service $out/etc/systemd/system/ipfs.service
-    install -D misc/systemd/ipfs-api.socket $out/etc/systemd/system/ipfs-api.socket
-    install -D misc/systemd/ipfs-gateway.socket $out/etc/systemd/system/ipfs-gateway.socket
+    install --mode=444 -D misc/systemd/ipfs.service $out/etc/systemd/system/ipfs.service
+    install --mode=444 -D misc/systemd/ipfs-api.socket $out/etc/systemd/system/ipfs-api.socket
+    install --mode=444 -D misc/systemd/ipfs-gateway.socket $out/etc/systemd/system/ipfs-gateway.socket
     substituteInPlace $out/etc/systemd/system/ipfs.service \
       --replace /usr/bin/ipfs $out/bin/ipfs
   '';