[dns-sd] add DNS-SD server network interface binding configuration(#6838)

This commit allows DNS-SD server to configure the network interface to
bind the UDP socket.

script/test

@@ -273,6 +273,7 @@ do_build_otbr_docker()
         "-DOT_SRP_CLIENT=ON"
         "-DOT_TREL=OFF"
         "-DOTBR_DUA_ROUTING=ON"
+        "-DCMAKE_CXX_FLAGS='-DOPENTHREAD_CONFIG_DNSSD_SERVER_BIND_UNSPECIFIED_NETIF=1'"
     )
     local otbr_docker_image=${OTBR_DOCKER_IMAGE:-otbr-ot12-backbone-ci}