IB/rxe: Make counters thread safe

Current rxe device counters are not thread safe.
When multiple QPs are used, they can be racy.
Make them thread safe by making it atomic64.

Fixes: 0b1e5b99 ("IB/rxe: Add port protocol stats")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>