RDMA/core: Rename kernel modify_cq to better describe its usage

Current ib_modify_cq() is used to set CQ moderation parameters.

This patch renames ib_modify_cq() to be rdma_set_cq_moderation(),
because the kernel version of RDMA API doesn't need to follow already
exposed to user's API pattern (create_XXX/modify_XXX/query_XXX/destroy_XXX)
and better to have more accurate name which describes the actual usage.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>