ggsn: Be able to set the log level for the text file

Fixes: SYS#599
diff --git a/ggsn/cmdline.ggo b/ggsn/cmdline.ggo
index 5bb05dc..9c4c976 100644
--- a/ggsn/cmdline.ggo
+++ b/ggsn/cmdline.ggo
@@ -32,4 +32,4 @@
 option  "apn"         a "Access point name"             string default="internet" no
 option  "qos"         q "Requested quality of service"  int    default="0x0b921f" no
 option  "logfile"     - "Logfile for errors"            string no
-
+option  "loglevel"    - "Global log ldevel"		string default="error" no