GDP-Man:Man2GlcNAc2-PP-Dolichol Alpha-1,6-Mannosyltransferase Activity

Catalysis of the reaction: GDP-alpha-D-mannose(2-) + a (mannosyl)2-(N-acetylglucosaminyl)2-diphosphodolichol <=> H+ + GDP(3-) + a (mannosyl)3-(N-acetylglucosaminyl)2-diphosphodolichol.