FwmarkCommand.h - fix uninitialized fields in constructor

Fixes:
  system/netd/include/FwmarkCommand.h:34:5: error: 2 uninitialized fields at the end of the constructor call [clang-analyzer-optin.cplusplus.UninitializedObject,-warnings-as-errors]
      FwmarkConnectInfo() {}
      ^
  system/netd/include/FwmarkCommand.h:26:9: note: uninitialized field 'this->error'
      int error;
          ^
  system/netd/include/FwmarkCommand.h:27:14: note: uninitialized field 'this->latencyMs'
      unsigned latencyMs;
               ^
  system/netd/server/FwmarkServer.cpp:103:23: note: Calling default constructor for 'FwmarkConnectInfo'
      FwmarkConnectInfo connectInfo;
                        ^

Test: builds
Bug: 155351989
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8f9f69e65d64462e790eadd25ec83bd2d0a82b16