support Knot DNS master (3.1)

ci/debian-11/Dockerfile

@@ -16,7 +16,7 @@ RUN apt-get update -qq
 RUN apt-get install -y -qqq git make cmake pkg-config meson \
 	build-essential bsdmainutils libtool autoconf libcmocka-dev \
 	liburcu-dev libgnutls28-dev libedit-dev liblmdb-dev libcap-ng-dev libsystemd-dev \
-	libelf-dev libidn11-dev libuv1-dev \
+	libelf-dev libmnl-dev libidn11-dev libuv1-dev \
 	libluajit-5.1-dev lua-http libssl-dev libnghttp2-dev
 
 # Build and testing deps for Resolver's dnstap module (go stuff is just for testing)