Dec 9 (Reuters) - Russian forces have shelled the entire front line in the Donetsk region in eastern Ukraine, Ukrainian officials said, part of what appears to be the Kremlin's scaled-back ambition to secure only the bulk of territory it has claimed. CONFLICT * The fiercest fighting was near the towns of Bakhmut and Avdiivka, and Russian troops were also trying to advance near Lyman, which was recaptured by Ukrainian forces in November, the region's governor Pavlo Kyrylenko said. * The Ukrainian general staff said its forces had attacked Russian positions and troop assembly points in at least half a...