Conditionalize Avahi Service Start and Installation (openthread#2280)

Ensure the Avahi daemon is installed and started only when
OTBR_MDNS == "avahi". This prevents multiple mDNS stacks from
running especially in container environments.

script/bootstrap

@@ -57,7 +57,12 @@ install_packages_apt()
     sudo apt-get install --no-install-recommends -y libdbus-1-dev
 
     # mDNS
-    sudo apt-get install --no-install-recommends -y libavahi-client3 libavahi-common-dev libavahi-client-dev avahi-daemon
+    sudo apt-get install --no-install-recommends -y libavahi-client3 libavahi-common-dev libavahi-client-dev
+
+    if [[ ${OTBR_MDNS} == "avahi" ]]; then
+      sudo apt-get install --no-install-recommends -y avahi-daemon
+    fi
+
     (MDNS_RESPONDER_SOURCE_NAME=mDNSResponder-1790.80.10 \
         && MDNS_RESPONDER_PATCH_PATH=$(realpath "$(dirname "$0")"/../third_party/mDNSResponder) \
         && cd /tmp \

script/server

@@ -47,15 +47,20 @@ startup()
     if have systemctl; then
         systemctl is-active rsyslog || sudo systemctl start rsyslog || die 'Failed to start rsyslog!'
         systemctl is-active dbus || sudo systemctl start dbus || die 'Failed to start dbus!'
-        systemctl is-active avahi-daemon || sudo systemctl start avahi-daemon || die 'Failed to start avahi!'
+        sudo service mdns status || sudo service mdns start || echo "service mdns is not available!"
+        if [[ ${OTBR_MDNS} == "avahi" ]]; then
+          systemctl is-active avahi-daemon || sudo systemctl start avahi-daemon || die 'Failed to start avahi!'
+        fi
         without WEB_GUI || systemctl is-active otbr-web || sudo systemctl start otbr-web || die 'Failed to start otbr-web!'
         systemctl is-active otbr-agent || sudo systemctl start otbr-agent || die 'Failed to start otbr-agent!'
     elif have service; then
         sudo service rsyslog status || sudo service rsyslog start || die 'Failed to start rsyslog!'
         sudo service dbus status || sudo service dbus start || die 'Failed to start dbus!'
         # Tolerate the mdns failure as it is installed for only CI docker.
         sudo service mdns status || sudo service mdns start || echo "service mdns is not available!"
-        sudo service avahi-daemon status || sudo service avahi-daemon start || die 'Failed to start avahi!'
+        if [[ ${OTBR_MDNS} == "avahi" ]]; then
+          sudo service avahi-daemon status || sudo service avahi-daemon start || die 'Failed to start avahi!'
+        fi
         sudo service otbr-agent status || sudo service otbr-agent start || die 'Failed to start otbr-agent!'
         without WEB_GUI || sudo service otbr-web status || sudo service otbr-web start || die 'Failed to start otbr-web!'
     else
@@ -73,14 +78,18 @@ shutdown()
     if have systemctl; then
         systemctl is-active rsyslog && sudo systemctl stop rsyslog || echo 'Failed to stop rsyslog!'
         systemctl is-active dbus && sudo systemctl stop dbus || echo 'Failed to stop dbus!'
-        systemctl is-active avahi-daemon && sudo systemctl stop avahi-daemon || echo 'Failed to stop avahi!'
+        if [[ ${OTBR_MDNS} == "avahi" ]]; then
+          systemctl is-active avahi-daemon && sudo systemctl stop avahi-daemon || echo 'Failed to stop avahi!'
+        fi
         without WEB_GUI || systemctl is-active otbr-web && sudo systemctl stop otbr-web || echo 'Failed to stop otbr-web!'
         systemctl is-active otbr-agent && sudo systemctl stop otbr-agent || echo 'Failed to stop otbr-agent!'
     elif have service; then
         sudo service rsyslog status && sudo service rsyslog stop || echo 'Failed to stop rsyslog!'
         sudo service dbus status && sudo service dbus stop || echo 'Failed to stop dbus!'
         sudo service mdns status && sudo service mdns stop || echo "service mdns is not available!"
-        sudo service avahi-daemon status && sudo service avahi-daemon stop || echo 'Failed to stop avahi!'
+        if [[ ${OTBR_MDNS} =="avahi" ]]; then
+          sudo service avahi-daemon status && sudo service avahi-daemon stop || echo 'Failed to stop avahi!'
+        fi
         sudo service otbr-agent status && sudo service otbr-agent stop || echo 'Failed to stop otbr-agent!'
         without WEB_GUI || sudo service otbr-web status && sudo service otbr-web stop || echo 'Failed to stop otbr-web!'
     else