gluon-status-page: suppress "broken pipe" syslog message

Some HTTP endpoints were writing annoying "broken pipe" messages to stderr.

package/gluon-status-page-api/files/lib/gluon/status-page/www/cgi-bin/dyn/neighbours-nodeinfo

@@ -8,6 +8,6 @@ badrequest() {
 
 echo 'Access-Control-Allow-Origin: *'
 
-batctl if | cut -d: -f1 | grep -qxF "$QUERY_STRING" || badrequest
+( batctl if | cut -d: -f1 | grep -qxF "$QUERY_STRING" ) 2>/dev/null || badrequest
 
 exec /usr/bin/gluon-neighbour-info -s neighbour -i "$QUERY_STRING" -d ff02::2:1001 -p 1001 -r nodeinfo

package/gluon-status-page-api/files/lib/gluon/status-page/www/cgi-bin/dyn/stations

@@ -8,7 +8,7 @@ badrequest() {
 
 echo 'Access-Control-Allow-Origin: *'
 
-batctl if | cut -d: -f1 | grep -qxF "$QUERY_STRING" || badrequest
+( batctl if | cut -d: -f1 | grep -qxF "$QUERY_STRING" ) 2>/dev/null || badrequest
 
 CMD="exec /lib/gluon/status-page/providers/stations '$QUERY_STRING'"