[dns] implement DNS query over TCP (#8474)

This commit introduces DNS query over TCP protocol.

tests/scripts/expect/cli-tcp-tls.exp

@@ -30,7 +30,10 @@
 source "tests/scripts/expect/_common.exp"
 source "tests/scripts/expect/_multinode.exp"
 
-setup_two_nodes
+spawn_node 2 "cli"
+spawn_node 1 "cli"
+setup_leader
+setup_node 2 "rnd" "router"
 
 switch_node 1
 send "tcp init tls\n"

tests/scripts/expect/cli-tcp.exp

@@ -30,7 +30,10 @@
 source "tests/scripts/expect/_common.exp"
 source "tests/scripts/expect/_multinode.exp"
 
-setup_two_nodes
+spawn_node 2 "cli"
+spawn_node 1 "cli"
+setup_leader
+setup_node 2 "rnd" "router"
 
 switch_node 1
 send "tcp init circular\n"

tests/scripts/expect/tun-dns-over-tcp-client.exp

@@ -0,0 +1,46 @@
+#!/usr/bin/expect -f
+#
+#  Copyright (c) 2020, The OpenThread Authors.
+#  All rights reserved.
+#
+#  Redistribution and use in source and binary forms, with or without
+#  modification, are permitted provided that the following conditions are met:
+#  1. Redistributions of source code must retain the above copyright
+#     notice, this list of conditions and the following disclaimer.
+#  2. Redistributions in binary form must reproduce the above copyright
+#     notice, this list of conditions and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#  3. Neither the name of the copyright holder nor the
+#     names of its contributors may be used to endorse or promote products
+#     derived from this software without specific prior written permission.
+#
+#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+#  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+#  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+#  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+#  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+#  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+#  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+#  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+#  POSSIBILITY OF SUCH DAMAGE.
+#
+
+source "tests/scripts/expect/_common.exp"
+source "tests/scripts/expect/_multinode.exp"
+
+spawn_node 2 "cli"
+spawn_node 1
+setup_leader
+setup_node 2 "rnd" "router"
+
+switch_node 1
+set addr_1 [get_ipaddr mleid]
+
+switch_node 2
+send "dns resolve ipv6.google.com $addr_1 2000 6000 4 1 tcp\n"
+expect "DNS response for ipv6.google.com"
+expect_line "Done"
+
+dispose_all