resolved: use standard paths for .dnssd files

/usr/local/lib/systemd/dnssd is now also included in the search path. This
path is of limited usefulness, but it makes sense to be consistent.

Documentation is updated to match. Outdated advice against drop-ins in /usr
is removed.

src/resolve/resolved-dnssd.c

@@ -2,21 +2,14 @@
 
 #include "conf-files.h"
 #include "conf-parser.h"
+#include "def.h"
 #include "resolved-dnssd.h"
 #include "resolved-dns-rr.h"
 #include "resolved-manager.h"
 #include "specifier.h"
 #include "strv.h"
 
-const char* const dnssd_service_dirs[] = {
-        "/etc/systemd/dnssd",
-        "/run/systemd/dnssd",
-        "/usr/lib/systemd/dnssd",
-#if HAVE_SPLIT_USR
-        "/lib/systemd/dnssd",
-#endif
-    NULL
-};
+#define DNSSD_SERVICE_DIRS ((const char* const*) CONF_PATHS_STRV("systemd/dnssd"))
 
 DnssdTxtData *dnssd_txtdata_free(DnssdTxtData *txt_data) {
         if (!txt_data)
@@ -93,7 +86,7 @@ static int dnssd_service_load(Manager *manager, const char *filename) {
 
         dropin_dirname = strjoina(service->name, ".dnssd.d");
 
-        r = config_parse_many(filename, dnssd_service_dirs, dropin_dirname,
+        r = config_parse_many(filename, DNSSD_SERVICE_DIRS, dropin_dirname,
                               "Service\0",
                               config_item_perf_lookup, resolved_dnssd_gperf_lookup,
                               false, service);
@@ -196,7 +189,7 @@ int dnssd_load(Manager *manager) {
         if (manager->mdns_support != RESOLVE_SUPPORT_YES)
                 return 0;
 
-        r = conf_files_list_strv(&files, ".dnssd", NULL, 0, dnssd_service_dirs);
+        r = conf_files_list_strv(&files, ".dnssd", NULL, 0, DNSSD_SERVICE_DIRS);
         if (r < 0)
                 return log_error_errno(r, "Failed to enumerate .dnssd files: %m");