in_syslog: honor source keys for unmatched lines

Include source_address_key or source_hostname_key on unmatched lines
when configured.

This fixes the test cases added in
e3b959b.

lib/fluent/plugin/in_syslog.rb

@@ -199,14 +199,22 @@ def start_tcp_server(tls: false)
 
     private
 
+    def emit_unmatched(data, sock)
+      record = {}
+      record[@source_address_key] = sock.remote_addr if @source_address_key
+      record[@source_hostname_key] = sock.remote_host if @source_hostname_key
+      record["unmatched_line"] = data
+      emit("#{@tag}.unmatched", Fluent::EventTime.now, record)
+    end
+
     def message_handler(data, sock)
       pri = nil
       text = data
       unless @parser_parse_priority
         m = SYSLOG_REGEXP.match(data)
         unless m
           if @emit_unmatched_lines
-            emit("#{@tag}.unmatched", Fluent::EventTime.now, {"unmatched_line" => data})
+            emit_unmatched(data, sock)
           end
           log.warn "invalid syslog message: #{data.dump}"
           return
@@ -218,7 +226,7 @@ def message_handler(data, sock)
       @parser.parse(text) do |time, record|
         unless time && record
           if @emit_unmatched_lines
-            emit("#{@tag}.unmatched", Fluent::EventTime.now, {"unmatched_line" => text})
+            emit_unmatched(data, sock)
           end
           log.warn "failed to parse message", data: data
           return
@@ -238,7 +246,7 @@ def message_handler(data, sock)
       end
     rescue => e
       if @emit_unmatched_lines
-        emit("#{@tag}.unmatched", Fluent::EventTime.now, {"unmatched_line" => text})
+        emit_unmatched(data, sock)
       end
       log.error "invalid input", data: data, error: e
       log.error_backtrace