RDMA/hns: Response dmac to userspace

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8HZ7W



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While creating AH, dmac is already resolved in kernel. Response dmac
to userspace so that userspace doesn't need to resolve dmac repeatly.

Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>