RDMA/rtrs: Require holding rcu_read_lock explicitly

No functional change. The function get_next_path_rr needs to hold
rcu_read_lock. As such, if no rcu read lock, warnings will pop out.

Acked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://lore.kernel.org/r/20230919073727.540207-1-yanjun.zhu@intel.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>