HANOI (Reuters) -The United States expects to elevate its diplomatic relations with former foe Vietnam to the top level as President Joe Biden travels to Hanoi in a week, in a move that may irk China and with unclear business implications. Fearful of the potential reaction from its much larger neighbour, Vietnam had initially expressed caution about the upgrade. The unprecedented push has led Washington to expect to be elevated to the top tier of Vietnam's diplomatic ranking, together with China and Russia, from two notches below now.