nqptp: copy systemd service and add capability

The binary has its capability to listen on ports removed, and upstream
has already moved to AmbientCapabilities in the systemd service instead
of using setcap. Copying the systemd service allows using the package
with `systemd.packages`.

The patch should be removed after version 1.2.4, along with the other
patch. The patch is taken from [commit 050a8c2][1] in the upstream
repository.

[1]: mikebrady/nqptp@050a8c2

pkgs/tools/networking/nqptp/default.nix

@@ -18,8 +18,9 @@ stdenv.mkDerivation rec {
   };
 
   patches = [
-    # this patch should be removed when > 1.2.4
+    # these patches should be removed when > 1.2.4
     ./remove-setcap.patch
+    ./systemd-service-capability.patch
   ];
 
   nativeBuildInputs = [ autoreconfHook pkg-config ];
@@ -28,6 +29,11 @@ stdenv.mkDerivation rec {
     ignoredVersions = ".*(-dev|d0)";
   };
 
+  postInstall = ''
+    mkdir -p $out/lib/systemd/system
+    cp nqptp.service $out/lib/systemd/system
+  '';
+
   meta = {
     homepage = "https://github.com/mikebrady/nqptp";
     description = "Daemon and companion application to Shairport Sync that monitors timing data from any PTP clocks";

pkgs/tools/networking/nqptp/systemd-service-capability.patch

@@ -0,0 +1,12 @@
+diff --git a/nqptp.service.in b/nqptp.service.in
+index 6f1eb0c..53e6a2e 100644
+--- a/nqptp.service.in
++++ b/nqptp.service.in
+@@ -8,6 +8,7 @@ Before=shairport-sync.service
+ ExecStart=@prefix@/bin/nqptp
+ User=nqptp
+ Group=nqptp
++AmbientCapabilities=CAP_NET_BIND_SERVICE
+
+ [Install]
+ WantedBy=multi-user.target