RDMA/hns: Get message length of ack_req from FW

RDMA/hns: Get message length of ack_req from FW

ACK_REQ_FREQ indicates the number of packets (after MTU fragmentation)
HW sends before setting an ACK request. When MTU is greater than or
equal to 1024, the current ACK_REQ_FREQ value causes HW to request an
ACK for every MTU fragment. The processing of a large number of ACKs
severely impacts HW performance when sending large size payloads.

Get message length of ack_req from FW so that we can adjust this
parameter according to different situations. There are several
constraints for ACK_REQ_FREQ:

1. mtu * (2 ^ ACK_REQ_FREQ) should not be too large, otherwise it may
   cause some unexpected retries when sending large payload.

2. ACK_REQ_FREQ should be larger than or equal to LP_PKTN_INI.

3. ACK_REQ_FREQ must be equal to LP_PKTN_INI when using LDCP
   or HC3 congestion control algorithm.

Fixes: 56518a603fd2 ("RDMA/hns: Modify the value of long message loopback slice")
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://patch.msgid.link/20250703113905.3597124-4-huangjunxian6@hisilicon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>