dnsmasq: add meta.mainProgram

pkgs/tools/networking/dnsmasq/default.nix

@@ -90,6 +90,7 @@ stdenv.mkDerivation rec {
     description = "An integrated DNS, DHCP and TFTP server for small networks";
     homepage = "https://www.thekelleys.org.uk/dnsmasq/doc.html";
     license = licenses.gpl2;
+    mainProgram = "dnsmasq";
     platforms = with platforms; linux ++ darwin;
     maintainers = with maintainers; [ eelco fpletz globin ];
   };