resolved: stop mdns/lnrr when config changes to disabled on reload

Currently on reload mdns/lnrr are enabled if they were disabled,
but not viceversa. Fix it.

Follow-up for 14a5217679

mkosi.conf

@@ -103,6 +103,7 @@ Packages=
         kmod
         less
         llvm
+        lsof
         lvm2
         man
         mdadm

src/resolve/resolved-link.c

@@ -651,13 +651,16 @@ int link_update(Link *l) {
                 r = manager_llmnr_start(l->manager);
                 if (r < 0)
                         return r;
-        }
+        } else
+                manager_llmnr_stop(l->manager);
+
 
         if (link_get_mdns_support(l) != RESOLVE_SUPPORT_NO) {
                 r = manager_mdns_start(l->manager);
                 if (r < 0)
                         return r;
-        }
+        } else
+                manager_mdns_stop(l->manager);
 
         link_allocate_scopes(l);
         link_add_rrs(l, false);

test/units/TEST-75-RESOLVED.sh

@@ -339,6 +339,7 @@ manual_testcase_02_mdns_llmnr() {
     # defaults to yes (both the global and per-link settings are yes)
     assert_in 'yes' "$(resolvectl mdns hoge)"
     assert_in 'yes' "$(resolvectl llmnr hoge)"
+    lsof -p "$(systemctl show --property MainPID --value systemd-resolved.service)" | grep -q ":mdns\|:5353"
     # set per-link setting
     resolvectl mdns hoge yes
     resolvectl llmnr hoge yes
@@ -379,6 +380,7 @@ manual_testcase_02_mdns_llmnr() {
         echo "LLMNR=no"
     } >/run/systemd/resolved.conf.d/mdns-llmnr.conf
     systemctl reload systemd-resolved.service
+    (! lsof -p "$(systemctl show --property MainPID --value systemd-resolved.service)" | grep -q ":mdns\|:5353")
     # set per-link setting
     resolvectl mdns hoge yes
     resolvectl llmnr hoge yes