9.0.x SplitDNS is not working

[masaori335]

On investigation of #7315, I found that SplitDNS is not working at master & 9.0.x with the same configs which I used for 8.1.x.

Debug log says the splitdns fallback to default dns resolver.

[Nov 13 16:18:29.545] [ET_NET 11] DEBUG: <SplitDNS.cc:186 (getDNSRecord)> (splitdns) Called SplitDNS::getDNSRecord(example.com)
[Nov 13 16:18:29.545] [ET_NET 11] DEBUG: <SplitDNS.cc:200 (getDNSRecord)> (splitdns) Fail to match a valid splitdns rule, fallback to default dns resolver

It looks like SplitDNS::findServer() always returns DNS_SRVR_UNDEFINED when the fast path is enabled (SplitDNS::m_bEnableFastPath).

[masaori335]

The removing TCL dependency change from HostLookup looks root cause.
a7d06b8

[masaori335]

With #7320 fix, the assertion of mutex in Continuation::handleEvent() is failed. Which is the same symptom as #7315 (crash on 8.1.x). Please note that the 8.1.x doesn't have the assertion.

(lldb) bt
* thread #2, name = '[ET_NET 0]', stop reason = signal SIGABRT
  * frame #0: 0x00007fff6e38633a libsystem_kernel.dylib`__pthread_kill + 10
    frame #1: 0x00007fff6e442e60 libsystem_pthread.dylib`pthread_kill + 430
    frame #2: 0x00007fff6e30d808 libsystem_c.dylib`abort + 120
    frame #3: 0x000000000006a04e libtscore.10.dylib`ink_abort(message_format="%s:%d: failed assertion `%s`") at ink_error.cc:99:3
    frame #4: 0x000000000006716c libtscore.10.dylib`::_ink_assert(expression="!mutex || mutex->thread_holding == this_ethread()", file="/Users/masaori/src/github.com/apache/trafficserver-asf-master/iocore/eventsystem/I_Continuation.h", line=218) at ink_assert.cc:37:3
    frame #5: 0x0000000100004f5c traffic_server`Continuation::handleEvent(this=0x000000000702f000, event=0, data=0x0000000000000000) at I_Continuation.h:218:5
    frame #6: 0x0000000100294914 traffic_server`DNSConnection::trigger(this=0x0000000007043c20) at DNSConnection.cc:88:12
    frame #7: 0x00000001003bd1fb traffic_server`NetHandler::waitForActivity(this=0x0000000003ec7080, timeout=39995000) at UnixNet.cc:534:27
    frame #8: 0x00000001003fe701 traffic_server`EThread::execute_regular(this=0x0000000003ec3000) at UnixEThread.cc:303:14
    frame #9: 0x00000001003feb7d traffic_server`EThread::execute(this=0x0000000003ec3000) at UnixEThread.cc:364:11
    frame #10: 0x00000001003fcd3b traffic_server`spawn_thread_internal(a=0x0000000000d17200) at Thread.cc:92:12
    frame #11: 0x00007fff6e443109 libsystem_pthread.dylib`_pthread_start + 148
    frame #12: 0x00007fff6e43eb8b libsystem_pthread.dylib`thread_start + 15