jsoninfo: fix crash in /interfaces when olsrd is using a net interface that is not up
jsoninfo: fix crash in /interfaces when olsrd is using a net interface that is not up

tdz/olsrd,diogomg/olsrd-binary-heap,servalproject/olsr,diogomg/olsrd-binary-heap,tdz/olsrd,diogomg/olsrd,ninuxorg/olsrd,acinonyx/olsrd,diogomg/olsrd-binary-heap,diogomg/olsrd-binary-heap,tdz/olsrd,servalproject/olsr,zioproto/olsrd,ninuxorg/olsrd,sebkur/olsrd,sebkur/olsrd,diogomg/olsrd-binary-heap,tdz/olsrd,nolith/olsrd,duydb2/olsr,servalproject/olsr,acinonyx/olsrd,servalproject/olsr,zioproto/olsrd,ninuxorg/olsrd,duydb2/olsr,diogomg/olsrd,zioproto/olsrd,cholin/olsrd,duydb2/olsr,servalproject/olsr,sebkur/olsrd,diogomg/olsrd,nolith/olsrd,duydb2/olsr,nolith/olsrd,duydb2/olsr,diogomg/olsrd-binary-heap,diogomg/olsrd-binary-heap,duydb2/olsr,cholin/olsrd,sebkur/olsrd,ninuxorg/olsrd,zioproto/olsrd,ninuxorg/olsrd,cholin/olsrd,acinonyx/olsrd,diogomg/olsrd,diogomg/olsrd,acinonyx/olsrd,duydb2/olsr,servalproject/olsr,nolith/olsrd,nolith/olsrd,sebkur/olsrd,cholin/olsrd,diogomg/olsrd,zioproto/olsrd,sebkur/olsrd,acinonyx/olsrd,diogomg/olsrd,tdz/olsrd,duydb2/olsr,cholin/olsrd