Logging fixes

* Fixed: [Error message seen twice in some cases](https://github.com/clicon/clixon/issues/325)
* Extended `-l` command-line option to all clixon commands with a `none` option, eg `-l n` directs logging to `dev/null`

apps/restconf/restconf_lib.c

@@ -572,7 +572,7 @@ restconf_uripath(clicon_handle h)
 
 /*! Drop privileges from root to user (or already at user)
  * @param[in]  h    Clicon handle
- * Group set to clicon to communicate with backend
+ * Group set to CLICON_SOCK_GROUP to communicate with backend
  */
 int
 restconf_drop_privileges(clicon_handle h)

apps/restconf/restconf_main_fcgi.c

@@ -268,7 +268,7 @@ usage(clicon_handle h,
 	    "\t-D <level>\t  Debug level\n"
     	    "\t-f <file>\t  Configuration file (mandatory)\n"
 	    "\t-E <dir> \t  Extra configuration file directory\n"
-	    "\t-l <s|f<file>> \t  Log on (s)yslog, (f)ile (syslog is default)\n"
+	    "\t-l <s|e|o|n|f<file>> \tLog on (s)yslog, std(e)rr, std(o)ut, (n)one or (f)ile (syslog is default)\n"
 	    "\t-p <dir>\t  Yang directory path (see CLICON_YANG_DIR)\n"
 	    "\t-y <file>\t  Load yang spec file (override yang main module)\n"
     	    "\t-a UNIX|IPv4|IPv6 Internal backend socket family\n"

apps/restconf/restconf_main_native.c

@@ -1402,7 +1402,7 @@ usage(clicon_handle h,
 	    "\t-D <level>\t  Debug level, overrides any config debug setting\n"
     	    "\t-f <file>\t  Configuration file (mandatory)\n"
 	    "\t-E <dir> \t  Extra configuration file directory\n"
-	    "\t-l <s|f<file>> \t  Log on (s)yslog, (f)ile (syslog is default)\n"
+	    "\t-l <s|e|o|n|f<file>> \tLog on (s)yslog, std(e)rr, std(o)ut, (n)one or (f)ile (syslog is default)\n"
 	    "\t-p <dir>\t  Yang directory path (see CLICON_YANG_DIR)\n"
 	    "\t-y <file>\t  Load yang spec file (override yang main module)\n"
     	    "\t-a UNIX|IPv4|IPv6 Internal backend socket family\n"