By Robin Emmott and Sabine Siebold BRUSSELS (Reuters) - Germany would take part in a potential NATO mission to help slow refugee flows in the Aegean Sea, the country's defence minister said on Wednesday, a day before the alliance is due to discuss a request for help in easing Europe's migration crisis. Struggling to stop refugees streaming into Greece despite a deal between Ankara and the European Union to combat the flows, Germany and Turkey surprised partners this week by saying they would raise the issue with NATO.