ABUJA, July 17 (Reuters) - Nigeria's President Bola Tinubu has asked the Senate for an extra 6.2 trillion naira ($4 billion) in funding to plug shortfalls in this year's national budget, according to a letter read to lawmakers on Wednesday. ($1 = 1,555.0000 naira) (Reporting by Camillus Eboh; Writing by MacDonald Dzirutwe; Editing by Hugh Lawson)