rxe_counter_name is used in rxe_hw_counters.c only. Make it static.

Fixes: 0b1e5b99 ('IB/rxe: Add port protocol stats')
Signed-off-by: NKamal Heib <kamalh@mellanox.com>
Reviewed-by: NYonatan Cohen <yonatanc@mellanox.com>
Signed-off-by: NLeon Romanovsky <leon@kernel.org>
Signed-off-by: NDoug Ledford <dledford@redhat.com>