By Christoph Steitz FRANKFURT (Reuters) -German utility Uniper on Tuesday reported a 3 billion euro ($3.2 billion) net loss for the first quarter, citing impairment charges related to its Russian unit Unipro and its involvement in the suspended Nord Stream 2 pipeline. Germany’s top importer of Russian gas said its operating performance was also negatively impacted by lower gas storage withdrawals, which resulted in lower profit but higher storage levels in the wake of potential disruptions of supplies. “We have deliberately made this shift in results to take advantage of market opportunities a…