iputils: apply proposed upstream patch to get rid of systemd dependency

This allows us to get rid of the hack and the systemd dependency and
thus reduces the rebuild closure whenever systemd changes.

pkgs/os-specific/linux/iputils/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchFromGitHub
+{ stdenv, fetchFromGitHub, fetchpatch
 , meson, ninja, pkgconfig, gettext, libxslt, docbook_xsl_ns
 , libcap, libidn2
 }:
@@ -22,11 +22,13 @@ in stdenv.mkDerivation rec {
     sha256 = "1jhbcz75a4ij1myyyi110ma1d8d5hpm3scz9pyw7js6qym50xvh4";
   };
 
-  postPatch = ''
-    # Enable the systemd units even without systemd being an input. We set the
-    # unitdir manually anyway.
-    sed -e 's/systemd\.found()/true/g' -i meson.build
-  '';
+  patches = [
+    # Proposed upstream patch to reduce dependency on systemd: https://github.com/iputils/iputils/pull/297
+    (fetchpatch {
+      url = "https://github.com/iputils/iputils/commit/13d6aefd57fd471ecad06e19073dcc44608dff5e.patch";
+      sha256 = "1n62zxmzp7hgz9qapbbpqv3fxqvc3qyd2a73jhp357x6by84kj49";
+    })
+  ];
 
   mesonFlags = [
     "-DBUILD_RARPD=true"
@@ -34,6 +36,7 @@ in stdenv.mkDerivation rec {
     "-DBUILD_TFTPD=true"
     "-DNO_SETCAP_OR_SUID=true"
     "-Dsystemdunitdir=etc/systemd/system"
+    "-DINSTALL_SYSTEMD_UNITS=true"
   ]
     # Disable idn usage w/musl (https://github.com/iputils/iputils/pull/111):
     ++ optional stdenv.hostPlatform.isMusl "-DUSE_IDN=false";