wireless: gs2200m: Add SIOCGIFFLAGS support to gs2200m_main.c

Summary:
- I noticed that the latest ifconfig command shows nothing
- Finally, I found that gs2200m_main.c needs to handle SIOCGIFFLAGS
- This commit fixes this issue

Impact:
- gs2200m only

Testing:
- Tested with spresense:wifi
- NOTE: gs2200m driver needs to be updated as well

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

wireless/gs2200m/gs2200m_main.c

@@ -1568,6 +1568,7 @@ static int ioctl_request(int fd, FAR struct gs2200m_s *priv,
   switch (req->cmd)
     {
       case SIOCGIFADDR:
+      case SIOCGIFFLAGS:
       case SIOCGIFHWADDR:
       case SIOCGIWNWID:
       case SIOCGIWFREQ: