fix ffrn-remove-old-vlan script to run under gluon

ffrn-remove-old-vlan/files/lib/gluon/upgrade/100-ffrn-remove-old-vlan

 #!/bin/sh
 
-sed -e "/config interface 'mesh_radio0_vlan'/,+4d" /etc/config/network
+sed -ie "/config interface 'mesh_radio0_vlan'/ { N;N;N;N;N; d; }" /etc/config/network