gateway: initialise the egress interface names in/for multi-gateway mode
gateway: initialise the egress interface names in/for multi-gateway mode

Signed-off-by: Ferry Huberts <66e11f9f5d965b69497c7e73d5e808f8b13c1218@pelagic.nl>
Reviewed-by: Henning Rogge <35b1cb25ad22a15c873242a24069a9b71f851b2d@googlemail.com>

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