Fix crash in HttpSM::tunnel_handler on unhandled VC events (#12959)

tunnel_handler is set as the VC read/write handler for the server
connection after response header parsing, but it only asserts for
HTTP_TUNNEL_EVENT_DONE and VC_EVENT_INACTIVITY_TIMEOUT. If a
VC_EVENT_ACTIVE_TIMEOUT, VC_EVENT_ERROR, or VC_EVENT_EOS arrives
on the server connection, the assertion fires and aborts the process.

Widen the assertion to accept these events. The handler already sets
terminate_sm = true for all events, so the behavior is correct — only
the assertion was too narrow.

Fixes #12958

Author: bryancall

src/proxy/http/HttpSM.cc

@@ -3136,7 +3136,8 @@ HttpSM::tunnel_handler(int event, void * /* data ATS_UNUSED */)
     return 0;
   }
 
-  ink_assert(event == HTTP_TUNNEL_EVENT_DONE || event == VC_EVENT_INACTIVITY_TIMEOUT);
+  ink_assert(event == HTTP_TUNNEL_EVENT_DONE || event == VC_EVENT_INACTIVITY_TIMEOUT || event == VC_EVENT_ACTIVE_TIMEOUT ||
+             event == VC_EVENT_ERROR || event == VC_EVENT_EOS);
   // The tunnel calls this when it is done
   terminate_sm = true;