TEST-21-DFUZZER: enable services to be tested

Since e19e17df57, timesyncd is disabled by
default, and fuzzing for timesyncd failed.

```
[  754.247451] TEST-21-DFUZZER.sh[658]: Bus: org.freedesktop.timesync1 (system)
[  754.247725] TEST-21-DFUZZER.sh[658]: + systemd-run --pipe --wait -- dfuzzer -b 10000 -n org.freedesktop.timesync1
[  754.282237] TEST-21-DFUZZER.sh[3236]: Running as unit: run-p3236-i3237.service
[  754.348983] TEST-21-DFUZZER.sh[3238]: [SESSION BUS]
[  754.350443] TEST-21-DFUZZER.sh[3238]: Bus not found.
[  754.350705] TEST-21-DFUZZER.sh[3238]: [SYSTEM BUS]
[  754.359249] TEST-21-DFUZZER.sh[3238]: Error while calling method 'GetConnectionUnixProcessID': GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: The connection does not exist
[  754.359520] TEST-21-DFUZZER.sh[3238]: Couldn't get the PID of the tested process
[  754.359764] TEST-21-DFUZZER.sh[3238]: Exit status: 4
[  754.386721] TEST-21-DFUZZER.sh[3236]:           Finished with result: exit-code
[  754.387331] TEST-21-DFUZZER.sh[3236]: Main processes terminated with: code=exited, status=4/NOPERMISSION
[  754.387537] TEST-21-DFUZZER.sh[3236]:                Service runtime: 74ms
[  754.387706] TEST-21-DFUZZER.sh[3236]:              CPU time consumed: 21ms
[  754.389210] TEST-21-DFUZZER.sh[3236]:                    Memory peak: 12.9M (swap: 0B)
```

Also, create dummy interface for networkd and resolved.

Fixes #37834.

test/units/TEST-21-DFUZZER.sh

@@ -126,37 +126,51 @@ cat /etc/dfuzzer.conf
 
 # TODO
 #   * check for possibly newly introduced buses?
-BUS_LIST=(
-    org.freedesktop.home1
-    org.freedesktop.hostname1
-    org.freedesktop.import1
-    org.freedesktop.locale1
-    org.freedesktop.login1
-    org.freedesktop.machine1
-    org.freedesktop.portable1
-    org.freedesktop.resolve1
-    org.freedesktop.timedate1
+NAME_LIST=(
+    home
+    hostname
+    import
+    locale
+    login
+    machine
+    portable
+    resolve
+    timedate
 )
 
-# systemd-oomd requires PSI
-if tail -n +1 /proc/pressure/{cpu,io,memory}; then
-    BUS_LIST+=(
-        org.freedesktop.oom1
-    )
-fi
-
 # Some services require specific conditions:
+#   - systemd-oomd requires PSI
 #   - systemd-timesyncd can't run in a container
 #   - systemd-networkd can run in a container if it has CAP_NET_ADMIN capability
+if tail -n +1 /proc/pressure/{cpu,io,memory}; then
+    NAME_LIST+=( oom )
+fi
+
 if ! systemd-detect-virt --container; then
-    BUS_LIST+=(
-        org.freedesktop.network1
-        org.freedesktop.timesync1
-    )
-elif busctl introspect org.freedesktop.network1 / &>/dev/null; then
-    BUS_LIST+=(
-        org.freedesktop.network1
-    )
+    NAME_LIST+=( timesync )
+fi
+
+if ip link add dummy-fuzz type dummy; then
+    # if a dummy interface is created, then let's also setup it for resolved
+    ip link set dummy-fuzz up
+    ip address add 192.0.2.1/24 dev dummy-fuzz
+
+    # When we can create a dummy interface, we definitely have CAP_NET_ADMIN
+    NAME_LIST+=( network )
+
+    # Create unit files for another dummy interface for networkd
+    mkdir -p /run/systemd/network
+    cat >/run/systemd/network/10-dummy-fuzz2.netdev <<EOF
+[NetDev]
+Kind=dummy
+Name=dummy-fuzz2
+EOF
+    cat >/run/systemd/network/10-dummy-fuzz2.network <<EOF
+[Match]
+Name=dummy-fuzz2
+[Network]
+Address=192.0.2.2/24
+EOF
 fi
 
 # Maximum payload size generated by dfuzzer (in bytes) - default: 50K
@@ -188,10 +202,24 @@ mount -t tmpfs -o size=50M tmpfs /var/lib/machines
 
 # Next, test the system service buses, as the services may be in a spurious
 # state after fuzzing the system service manager bus.
-for bus in "${BUS_LIST[@]}"; do
+for name in "${NAME_LIST[@]}"; do
+    bus="org.freedesktop.${name}1"
+    service="systemd-${name}d.service"
+
     echo "Bus: $bus"
+
+    # Unmask and enable the service.
+    systemctl unmask "$service"
+    systemctl enable "$service"
+
+    # enable debugging logs
+    systemctl service-log-level "$service" debug || :
+
     systemd-run --pipe --wait \
                 -- dfuzzer -b "$PAYLOAD_MAX" -n "$bus"
+
+    # disable debugging logs
+    systemctl service-log-level "$service" info || :
 done
 
 umount /var/lib/machines