[gdb/dap] Add logging of ignored lines

[gdb/dap] Add logging of ignored lines

This input sequence is accepted by DAP:
...
{"seq": 4, "type": "request", "command": "configurationDone"}Content-Length: 84
...

This input sequence has the same effect:
...
{"seq": 4, "type": "request", "command": "configurationDone"}ignorethis
Content-Length: 84
...
but the 'ignorethis' part is silently ignored.

Log the ignored bit, such that we have:
...
READ: <<<{"seq": 4, "type": "request", "command": "configurationDone"}>>>
WROTE: <<<{"request_seq": 4, "type": "response", "command": "configurationDone"
, "success": true}>>>
+++ run
IGNORED: <<<b'ignorethis'>>>
...