RDMA/bnxt_re: Validate rate limit attribute in modify QP

RDMA/bnxt_re: Validate rate limit attribute in modify QP

Rate limit transition validation for RC QPs currently relies on
the IB core qp_state_table. Add a driver-level helper to validate
the rate limit attribute directly during QP modify, ensuring it
is only accepted for RC QPs in INIT->RTR, RTR->RTS and RTS->RTS
transitions.

This makes the driver responsible for rate limit validation
and prepares for a follow-up IB core change that delegates
IB_QP_RATE_LIMIT and all future non-standard modify attributes
handling to individual vendor drivers.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20260524-packet-pacing-v1-6-3d79439f8d08@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>